WO2025104348A1

WO2025104348A1 - Water treatment

Info

Publication number: WO2025104348A1
Application number: PCT/EP2024/082747
Authority: WO
Inventors: Jaakko EKMAN; Patricia Aubeuf-Prieur; Marko Kolari
Original assignee: Kemira Oyj
Current assignee: Kemira Oyj
Priority date: 2023-11-17
Filing date: 2024-11-18
Publication date: 2025-05-22
Anticipated expiration: 2026-05-17

Abstract

Provided herein is a disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising: (i) treating the water to reduce phosphorus to a concentration of 0.7 mg/1 or less; and (ii) contacting the water treated in (ii) with an amount of percarboxylic acid to provide the disinfection. Also provided herein is a disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising contacting the water with an amount of percarboxylic acid to provide the disinfection, wherein the amount of percarboxylic acid is controlled based on the concentration of phosphorus in the water, and optionally also the concentration of total suspended solids in the water. Also provided herein are an apparatus and a system related to the methods, and use of a phosphorus precipitation and/or coagulation agent to reduce the amount of a percarboxylic acid required to disinfect water comprising at least one microorganism.

Description

WATER TREATMENT

Field of the Invention

The present disclosure generally relates to a method of treating water. The disclosure relates particularly, though not exclusively, to disinfection methods, apparatus and systems for optimising disinfection performance of a percarboxylic acid in a water treatment process. The present disclosure further relates to a use of a phosphorus precipitation and/or coagulation agent to improve disinfection performance of a percarboxylic acid in a water treatment process.

Background of the Invention

The need for purified water is increasing rapidly around the world. Efforts are being made to purify water using lower concentrations of chemical disinfectants, without, however, considerably raising the cost of the purification process. In addition, there is a need for the use of biodegradable or otherwise less harmful chemicals having fewer detrimental health effects.

Chlorine-based disinfectants (for example, hypochlorite, chlorine dioxide and chloramines) have traditionally been used to disinfect water, including wastewater. Chlorine-based disinfectants are quite effective against bacteria, but have lower efficiency against viruses, bacterial spores and protozoan cysts. In addition, chlorine-based disinfectants give rise to potentially toxic and mutagenic by-products, making them less desirable for use in disinfection processes.

Therefore, alternative disinfection methods have been considered. Among those, ultraviolet (UV) irradiation is currently the most widely used alternative disinfection method. It is typically efficient against enteric bacteria, viruses, parasite cysts and bacterial spores, and does not produce harmful by-products. However, if the UV dose is too low, photo-reactivation can occur, leading to potential regrowth under favourable conditions. Furthermore, UV-disinfection systems are highly dependent on upstream conventional treatment processes: UV is efficient only if the treated water quality is high (i.e. with low turbidity), as suspended solids can shield microorganisms from UV light. In addition, UV disinfection methods are relatively energy-intensive and expensive. Other alternative disinfection methods such as ozonation, ultrasound and membrane filtration have been studied. However, these methods are generally more expensive and have their own drawbacks.

The organic peroxides peracetic acid and performic acid have more recently been considered as alternative disinfectants.

Peracetic acid (PAA or CH3COOOH) is a broad-spectrum disinfectant with a high oxidationreduction (redox) potential. PAA is commercially available as an acidic quaternary equilibrium mixture with acetic acid, hydrogen peroxide (H2O2), and water as illustrated in reaction (1) below:

CH3COOH + H2O2 CH3CO-OOH + H₂O (1)

PAA is active against a wide spectrum of microorganisms. Disinfection mechanisms of PAA are based on the release of highly reactive oxygen species (ROS) such as hydroxyl (HO»), alkoxyl (RO»), hydroperoxyl (HO2*) and superoxide (02* ) radicals. The ROS can alter the metabolism of microbes and damage the structure of microbial cells, which occurs due to chain reactions between the ROS and biomolecules such as enzymes, lipids, structural proteins and DNA. PAA advantageously produces little to no toxic/mutagenic by-products after reaction with organic material, and degrades to acetic acid, hydrogen peroxide and water.

Performic acid (PFA or HC000H) has been used to disinfect primary and secondary wastewater treatment plant effluents (see below for description of wastewater treatment processes). PFA is normally applied as an equilibrium mixture of PFA, water, hydrogen peroxide and formic acid, as illustrated in reaction (2) below:

CHO-OH + H2O2 CH0-00H + H₂0 (2)

PFA is very unstable and typically needs to be generated on-site, shortly prior to use. The disinfection mechanisms of PFA are thought to be analogous to PAA via generation of ROS. PFA is considered to be more effective in disinfection than PAA (for example, requiring lower doses and/or shorter contact times) for inactivating at least some microorganisms including E. coli and Enterococcus. This may be attributable to the higher redox potential of PFA which provides a greater capacity to oxidise contaminants. Analogously to PAA, PF A produces little to no toxic/mutagenic by-products after reaction with organic materials. PFA is fully biodegradable and degradation products of PFA include carbon dioxide and water (Gehr et al., 2009, Water Sci. Technol. 59, 89-96).

There remains a need to improve the disinfection performance of organic peroxides such as PAA and PFA in order to increase the overall efficiency of water treatment systems and reduce operational costs.

Summary of the Invention

Accordingly, in a first aspect, the present invention provides a disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising:

(i) treating the water to reduce phosphorus to a concentration of 0.7 mg/1 or less; and

(ii) contacting the water treated in (i) with an amount of percarboxylic acid to provide the disinfection.

In a second aspect, the present invention provides a disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising contacting the water with an amount of percarboxylic acid to provide the disinfection, wherein the amount of percarboxylic acid is controlled based on the concentration of phosphorus in the water, and optionally also the concentration of total suspended solids in the water.

In a third aspect, the present invention provides an apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform a method of the invention. In a fourth aspect, the present invention provides a water treatment system comprising the apparatus of the invention, the system comprising: a first dosing device which is configured to feed into the water an agent that is a precipitation and/or coagulation agent to form a phosphorus precipitate and/or coagulate, a second dosing device which is configured to feed a percarboxylic acid to the water, and a first measuring device which is configured to measure the concentration of phosphorus in the water and generate output data relating to the measured concentration of the phosphorus, wherein the apparatus is constructed and arranged to receive the output data relating to the measured concentration of the phosphorus from the first measuring device, monitor the measured concentration of the phosphorous in the water, and to adjust the amount of the agent that is fed into the water by the first dosing device and/or adjust the amount of the percarboxylic acid that is fed to the water by the second dosing device based on the measured concentration of the phosphorus.

In a fifth aspect, the present invention provides use of precipitation and/or coagulation agent to reduce the amount of a percarboxylic acid required to disinfect water comprising at least one microorganism, wherein the water further comprises a concentration of phosphorus present as inorganic phosphates and/or as organic phosphorus, and wherein the use comprises reducing the concentration of the phosphorus in the water by contacting the water with the precipitation and/or coagulation agent to precipitate and/or coagulate the phosphorus and separating the precipitate and/or coagulate from the water.

Preferred features of all aspects of the present invention are defined in the dependent claims.

The methods, apparatus, system and use defined herein are particularly useful in wastewater treatment. The present inventors have found that both the amount of phosphorus (present as inorganic phosphates and/or as organic phosphorus) and the amount of total suspended solids in the water to be treated impact the amount of percarboxylic acid that it is necessary to use in order to achieve a desired level of disinfection. In particular, water comprising higher levels of these components requires more percarboxylic acid in order to achieve sufficient disinfection of the water.

Accordingly, in a water treatment process the amount of percarboxylic acids used in a disinfection step can be controlled based on the concentration of phosphorus and/or phosphate, and optionally also on the concentration of total suspended solids, in the water. Alternatively, or in addition, steps can be taken to reduce the concentration of phosphorus (as inorganic phosphates and/or organic phosphorus), and optionally also the concentration of total suspended solids in the water prior to disinfection, in order to increase the efficiency of the percarboxylic acid treatment step. Through this reduction the disinfection ability of the percarboxylic acid is advantageously improved. This, in turn, enables a reduced concentration of the percarboxylic acid to be used to achieve satisfactory disinfection and compliance with microbial reduction targets, with a consequent reduction in operational costs.

Brief Description of Figures

To assist understanding of the present disclosure and to show how embodiments may be put into effect, reference is made, by way of example only, to the accompanying Figures in which:

Figure 1 is a graph showing the amount of PFA in mg/1 necessary for efficient disinfection in wastewater samples with different concentrations of total suspended solids (TSS) in mg/1.

Figure 2 is a graph showing the amount of PFA in mg/1 necessary for efficient disinfection in wastewater samples comprising different concentrations of phosphorus (present in the samples as inorganic phosphates and organic phosphorus) in mg/1.

Figure 3 is a schematic block diagram illustrating an apparatus according to an example of the invention.

Detailed Description of the Invention

The present inventors have found that the level of phosphorus (present as inorganic phosphates and/or as organic phosphorus) in water requiring disinfection has an impact on the efficiency of disinfection with a percarboxylic acid; in water with higher concentrations of phosphorus more percarboxylic acid is required in order to achieve efficient disinfection.

Accordingly, the present invention provides a disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising:

Further, the present invention provides a disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising contacting the water with an amount of percarboxylic acid to provide the disinfection, wherein the amount of percarboxylic acid is controlled based on the concentration of phosphorus in the water. Optionally, the amount of percarboxylic acid can also be controlled based on the concentration of total suspended solids (TSS) in the water, as the inventors have also found that the level of TSS in water requiring disinfection has an impact on the efficiency of disinfection with percarboxylic acid.

Phosphorus can be present in the water to be disinfected both as free inorganic phosphates (e.g. in wastewater as a result of fertilizer in land runoff or from household detergents) and as part of organic matter (e.g. as part of phosphorus-accumulating microorganisms). In the present invention the concentration/amount of phosphorus refers to the total phosphorus in the water (including both phosphorus present as dissolved inorganic “free” phosphates and as phosphorus in a particulate state, organic form).

The total suspended solids (TSS) of a water sample refers to the suspended particles that are not dissolved in the water and which can be trapped by a filter. This includes both organic and inorganic suspended material. In some aspects and embodiments of the methods of the invention, control of the amount of percaboxylic acid that is contacted with the water is based on the concentration of phosphorus (present as inorganic phosphates and/or as organic phosphorus) in the water, and optionally also on the amount of TSS in the water to be treated. These concentrations of organic phosphorus / inorganic phosphates / TSS can be estimated or predicted concentrations (based on pre-existing knowledge of the water to be treated and/or direct measurements of related factors), or measured amounts, although preferably the concentrations are measured concentrations.

Methods to measure the concentration of organic phosphorus / phosphates present in water such as wastewater are known in the art. For example, the concentration can be measured by colorimetry-based methods, such as those used by commercially available automatic online analysers. Total phosphorus in a sample can be measured by methods such as USEPA1 PhosVer® 3 with Acid Persulfate Digestion Method by Hach Company, which converts organic phosphorus to phosphates and then measures the total phosphates in the sample. Total phosphates can be measured by USEPA PhosVer 3® (Ascorbic Acid) Method also by Hach Company.

The TSS of a water sample can also be measured by methods known in the art. For example, a sample of the water can be passed through a filter of a specific pore size (preferably 1.6 pm) and having a known weight, the filter and the captured material is then dried to remove the water from the filter, and the filter is then re-weighed to establish the weight of TSS captured. (A suitable method is provided in Example 1.)

Accordingly, in one embodiment the methods of the invention comprise measuring (a) the concentration of phosphorus in the water and/or (b) the concentration of total suspended solids in the water. Such measuring can be done offline, where a sample of the water is taken and analysed in a separate process alongside or away from the water being treated. However, preferably the measuring is done inline or online. Inline and online measurements are both forms of in situ measurement. Online measurements are not made directly in the main process line, but rather in a built-in branch or by-pass (for example, a sampling loop) into which samples of the water to be treated are automatically fed. Inline measurements are made directly in the main process line which requires placing a probe or sampling interface (or having a probe or sampling interface already positioned) directly into or in line with the process flow. For measurement methods requiring additional reagents to measure organic phosphorus / phosphates / TSS levels (for example, colorimetric methods as described above), online measurement configurations are preferred.

The measuring in the method of the invention may be done once, or at regular or irregular intervals. (In particular this can be done where the method comprises treating water that is in a continuous or semi-continuous flow.) For example, the concentrations in the water may be measured at regular intervals from 1 minute to 5 minutes, or at regular intervals of 10 minutes, 20 minutes, 30 minutes, every hour, every 2 hours, every 4 hours, every 6 hours, every 12 hours, every 24 hours. Alternatively, the concentrations may be measured at least once every half an hour to at least once a week. Preferably the concentration of phosphorus is measured at least once a day. Preferably the concentration of TSS is measured at least once every half an hour.

In preferred embodiments the measurement comprises measuring the concentration of inorganic phosphates in the water.

In one aspect/embodiment of the invention the methods comprise treating the water to reduce the concentration of phosphorus, and optionally also treating the water to reduce the concentration of total suspended solids, prior to using the percarboxy lie acid. For example, treating the water to reduce the concentration of phosphorus may comprise precipitation, coagulation, biological removal, and/or physical removal of phosphorus. Preferably, the treating comprises contacting the water with an agent that is a precipitation and/or coagulation agent to form a phosphorus precipitate and/or a phosphorus coagulate, and removing the precipitate and/or coagulate with sedimentation and/or filtration. The same agent may act to both precipitate and coagulate, and either mechanism is suitable for the present invention. For example, an agent that causes precipitation of phosphorus present as inorganic phosphates in the water may also cause coagulation of organic matter comprising organic phosphorus. In one embodiment the treatment comprises contacting the water with a source of calcium, iron, aluminium, or rare earth metal ions which act as precipitation/coagulation agents to achieve phosphorus precipitation/coagulation. Preferably the water is contacted with a source of iron and/or aluminium ions. The precipitate/coagulate formed in this way can be removed by sedimentation and/or filtration. Alternatively, or in addition, the method may comprise treating the water to reduce the concentration of phosphorus using microorganisms to assimilate or remove phosphorus from the water. This can be followed by further steps to remove the microorganisms from the water.

The concentration of phosphorus (i.e. phosphorus comprising organic phosphorus and inorganic phosphates) is reduced to 0.7 mg/1 or less, 0.5 mg/1 or less, preferably 0.3 mg/1 or less, more preferably 0.1 mg/1 or less prior to contacting the water with the amount of percarboxylic acid. Alternatively, the concentration of phosphorus is reduced to 0.03 to 0.7 mg/1, 0.03 to 0.5 mg/1, preferably 0.03 to 0.3 mg/1, more preferably to 0.03 to 0.1 mg/1 prior to contacting the water with the amount of percarboxylic acid.

Where the method comprises treating the water to reduce the amount of total suspended solids this treatment may comprise one or more of screening, agglomeration, sedimentation, biofiltration, and treatment in an oxidation pond. Suitable chemicals for use in reducing TSS in wastewater are known in the art. For example, typical chemicals include polymers, e.g. polyacrylamides, that can be used to cause flocculation of smaller particles to form larger solids, and metal ions, such as iron or aluminium, that can be used to cause coagulation of the TSS. The larger particles produced are easier to remove by physical separation techniques such as straining, sedimentation, and filtering.

Preferably the concentration of the total suspended solids is reduced to 20 mg/1 or less, preferably 10 mg/1 or less prior to contacting the water with the amount of percarboxylic acid. Alternatively, the concentration of TSS is reduced to 0.1 mg/1 to 20 mg/1, or preferably 0.1 mg/1 to 10 mg/1 prior to contacting the water with the amount of percarboxylic acid. As indicated above, the concentration of TSS can be determined for example using a filter of pore size 1.6 pm.

Disinfection

Regardless of the disinfection technology, disinfection performance is primarily governed by the concentration of residual disinfectant. The term “concentration of residual disinfectant” as used herein refers to the concentration of disinfectant after a period of contact with (or exposure to) water to be treated. Thus, if a threshold concentration of residual disinfectant is dynamically maintained during the disinfection process, then consistent disinfection performance will be met. In the disinfection method of the present invention contacting the water with percarboxylic acid comprises adding the percarboxylic acid to the water. As described above, in the method of the present invention the amount of percarboxylic acid contacted with the water can be controlled based on the concentration of phosphorus in the water, i.e. the amount of percarboxylic acid added to the water is controlled based on the concentration of phosphorus in the water. Optionally, the amount of percarboxylic acid contacted with the water can also be controlled based on the concentration of TSS in the water.

Clearly the amount of water is also to be taken into account in relation to determining the amount of percarboxylic acid contacted with the water in the method of the invention since the purpose is to provide disinfection. In particular, in the method of the invention the amount of percarboxylic acid is controlled based on the amount of water being treated. More particularly, where the method of the invention relates to disinfection of flowing water, the amount of water being treated is determined based on the flow rate of the water, i.e. the flow rate can be used to determine the amount of percarboxylic acid that is contacted with the water.

In one embodiment of the invention, the amount of percarboxylic acid contacted with the water is controlled based only on the amount, e.g. volume, flow rate, etc., of the water and the concentration of phosphorus in the water. In another embodiment, the amount of percarboxylic acid contacted with the water is controlled based only on the amount, e.g. volume flow rate of the water, the concentration of phosphorus, and the concentration of TSS in the water.

In other embodiments, a number of other factors are also used to determine the disinfection treatment with percarboxylic acid. In particular, it is already known that variations in water quality and quantity, as well as numerous side reactions between the disinfectant and water contaminants, may reduce the concentration of residual disinfectant, and consequently have an adverse effect on disinfection performance. For example, when added to wastewater, PFA and PAA undergo an initial rapid consumption (i.e. instantaneous disinfectant demand) followed by a more gradual decay. Poor water quality and water contaminants may accelerate the initial consumption and subsequent decay. As a result, these features may also need to be taken into account in controlling the of the amount of percarboxylic acid contacted with the water. The disinfection method of the invention may comprise a single addition of the percarboxylic acid that is controlled based on the concentration of phosphorus/phosphate and/or the concentration of TSS. Alternatively, the disinfection method may comprise multiple additions of percarboxylic acid to the water and one or more of these additions may be controlled based on the concentration of phosphorus and/or the concentration of TSS in the water to be treated. Still further, the disinfection method may comprise continuous addition of percarboxylic acid to the water and the control may comprise one or more adjustments of the amount and/or rate of addition of the percarboxylic acid during a period of continuous addition.

The percarboxylic acid may be contacted with the water (i.e. to achieve a concentration at the point of addition) in an amount of 0.1 to 8 mg/1, preferably 0.1 to 6 mg/1, and more preferably 0.2 to 4 mg/1. Particularly, where the percarboxylic acid is performic acid the performic acid may be contacted with the water in an amount from 0.1 to 2 mg/1, preferably 0.1 to 1.5 mg/1, and more preferably 0.2 to 1 mg/1. Where the percarboxylic acid is peracetic acid the peracetic acid may be contacted with the water in an amount from 0.4 to 8 mg/1, preferably 0.4 to 6 mg/1, and more preferably 0.8 to 4 mg/1.

Water to be treated

The water to be treated is not particularly limited, and is any water or aqueous solution in need of disinfection treatment, i.e. because it comprises at least one microorganism. The water to be treated may include raw water (for example, surface water from a lake, sea or river), drain water, water used in agriculture, rain water, wastewater, including municipal wastewater or industrial wastewater, or any mixtures of the above. In some examples, the water may comprise industrial wastewater. In this context, the term “industrial” may refer to pulp and paper industry, oil industry, mining industry, food industry, or to any other applicable industry. The water to be treated typically includes one or more contaminants such as bacteria, viruses, and other non-living organic matter.

Wastewater treatment

In preferred examples, the water to be treated comprises wastewater. Accordingly, the disinfection method according to the invention may be conducted within a wastewater treatment system or plant. The wastewater to be treated may include municipal wastewater, sewage and/or industrial wastewater.

Municipal wastewater or sewage treatment generally involves the following sequential processes: preliminary, primary, secondary and tertiary treatments. These are well-known to a person skilled in the art of wastewater treatment and water purification, and are discussed further below.

A preliminary treatment may remove coarse and large suspended materials that can be easily collected from the raw sewage or wastewater, for example, by screening and/or comminution, before they damage or obstruct any pumps and sewage lines of primary treatment apparatuses.

The primary treatment is designed to remove gross, suspended and floating solids from raw sewage or wastewater. Primary treatment may include screening to trap solid objects and sedimentation by gravity to remove suspended solids (removed and collected as sludge). The sedimentation process may be accelerated through the use of chemicals. The total suspended solids (TSS) concentration is an effective indicator of primary treatment. The TSS represents the weight proportion of fine particulate matter that remains in suspension per unit volume of water. Primary treatment may reduce the TSS concentration to 40 to 50%.

After the primary treatment, the wastewater may be directed to a secondary treatment which typically includes biological treatment steps and sedimentation. Specifically, primary effluent may be subjected to an activated sludge technique in which the effluent is aerated, and aerobic microorganisms metabolise organic matter to carbon dioxide and water and reproduce to form a microbial community. Organic nitrogen compounds may be converted to ammonia and subsequently nitrate. A secondary sedimentation tank may allow the microorganisms and solid wastes to agglomerate and settle as sludge. At least some of the collected sludge (activated sludge) may then be recycled for use as an inoculum for biological treatment of further incoming wastewater.

The secondary treatment may reduce the TSS content to 10 to 15%. The Biochemical Oxygen Demand (BOD) is a further indicator of secondary treatment. The BOD is a measure of the amount of oxygen needed or demanded by aerobic microorganisms to break down the organic matter present in a certain sample of water at a specific temperature and over a given time period. Secondary treatment typically reduces the BOD to 10 to 15%.

Alternative or additional processes carried out during secondary treatments may include biofiltration and oxidation ponds. Biofiltration requires the use of microorganisms immobilised on filters (e.g. sand filters, contact filters or trickling filters) to decompose organic matter and remove additional sediment. Oxidation ponds involve passing wastewater through large bodies of water (e.g. lagoons) in sunlight for extended periods of time to enable microorganisms to decompose organic matter.

Primary and secondary treatments are often sufficient for many purposes and not all wastewater treatment plants use tertiary treatment. Those that do use tertiary treatment achieve more stringent levels of cleanliness to meet the exacting standards that govern water reuse, especially in public water supplies. Tertiary treatment is also beneficial when facilities must discharge water into sensitive or fragile ecosystems (for example, estuaries, low-flow rivers, coral reefs, etc). Tertiary treatment may include filtration, disinfection and removal of nitrogen and phosphorus.

In view of the above, the method of the invention may comprise performing primary treatment and/or secondary treatment of the wastewater. In particular, such treatments can comprise reducing the concentration of TSS and/or the concentration of phosphorus (as described above) in the water prior to disinfection with the percarboxylic acid. Preferably such treatments comprise treating an influent of secondary sedimentation to reduce (a) the concentration of phosphorus in the water, and optionally also (b) the concentration of total suspended solids in the water, prior to contacting the water with the percarboxylic acid. In particular, the treatment may comprise contacting the influent of secondary sedimentation with a source of iron ions simultaneously or subsequent to aeration of the influent to achieve phosphorus precipitation, and removal of the precipitate with sedimentation and/or filtration. The method may then further comprises performing tertiary treatment of the wastewater, wherein contacting the water with the percarboxylic acid to provide the disinfection is performed during tertiary treatment.

Apparatus

In a further aspect the present invention provides an apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the method of the invention.

In particular, the apparatus may be regarded as a control apparatus for controlling at least a part of a disinfection method.

Figure 3 is a block diagram of an apparatus (18) according to an example of the invention. The control apparatus (18) is suitable for implementing at least some of the operations described herein. With specific reference to Figure 3, the apparatus (18) comprises at least one processor (28), at least one memory (29), a communication interface (32) and a user interface (31). The control apparatus may further comprise other internal circuitry and components necessary to perform the tasks described herein. The apparatus is arranged to use data regarding the concentration of phosphorus in the water and/or data regarding the concentration TSS in the water to control the amount of percarboxylic acid that is contacted with the water to provide the disinfection. In particular, the apparatus is arranged to control the amount of percarboxylic acid added to the water from a dosing device (14).

In relation to the data regarding the concentration of phosphorus in the water to be treated, the apparatus (18) is arranged to receive output data from a first measuring device (11) which measures the concentration of phosphorus in water. Optionally, in relation to the data regarding the concentration TSS in the water to be treated, the apparatus (18) is arranged to receive output data from a third measuring device (13) which measures the concentration of TSS in water. In addition, the apparatus (18) is arranged to receive output data from a second measuring device (12) which is configured to measure the concentration of percarboxylic acid in the water.

The apparatus (18) may comprise a communication interface (32) for connecting the control apparatus to a data communications system and enabling data communications with the apparatus. The communication interface (32) may comprise a wired and/or wireless communication circuitry, such as Ethernet, Wireless LAN, Bluetooth, GSM, CDMA, WCDMA, LTE, 5G circuitry, and/or analog. The communication interface can be integrated in the control apparatus (18) or provided as a part of an adapter, card or the like, that is attachable to the control apparatus (20). The communication interface (32) may support one or more different communication technologies. The apparatus (18) may also or alternatively comprise more than one communication interface

(32).

The user interface (31) may comprise a circuitry for receiving input from a user of the control apparatus (18), for example, via a keyboard, graphical user interface shown on the display of the apparatus, speech recognition circuitry, or an accessory device, such as a headset, and for providing output to the user via, for example, a graphical user interface or a loudspeaker. The apparatus may be operated remotely.

The at least one processor (28) may be coupled to the at least one memory (29). The at least one processor (28) may be configured to execute an appropriate computer program code to implement one or more of the aspects described herein. The at least one processor (28) may be a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), a graphics processing unit, an application specific integrated circuit (ASIC), a field programmable gate array, a microcontroller or a combination of such elements.

The at least one memory (29) may comprise a work memory (30) and a persistent (non-volatile, N/V) memory (33) configured to store computer program code (34) and data (35). The memory

(33) may comprise any one or more of: a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), a random-access memory (RAM), a flash memory, a data disk, an optical storage, a magnetic storage, a smart card, a solid state drive (SSD), or the like. The apparatus (18) may comprise other possible components for use in software- and hardware- aided execution of tasks it is designed to perform.

The apparatus (18) may comprise a plurality of memories (33). The memory (33) may be constructed as a part of the control apparatus (18) or as an attachment to be inserted into a slot, port, or the like of the apparatus (18) by a user or by another person or by a robot. The memory (33) may serve the sole purpose of storing data, or be constructed as a part of an apparatus (18) serving other purposes, such as processing data.

The skilled person would understand that in addition to the elements shown in Figure 3, the control apparatus (18) may comprise other elements, such as microphones, displays, as well as additional circuitry such as an input/output (I/O) circuitry, memory chips, application-specific integrated circuits (ASIC), a processing circuitry for specific purposes such as a source coding/decoding circuitry, a channel coding/decoding circuitry, a ciphering/deciphering circuitry, and the like. Additionally, the control apparatus (18) may comprise a disposable or rechargeable battery (not shown) for powering the apparatus (18) if an external power supply is not available. Further, it is noted that only one apparatus (18) is shown in Figure 3, but certain embodiments may equally be implemented in a cluster of shown apparatuses.

System

In a further aspect the present invention provides a water treatment system comprising the apparatus described above, the system comprising: a first dosing device which is configured to feed into the water an agent that is a precipitation and/or a coagulation agent to form a phosphorus precipitate and/or coagulate, a second dosing device which is configured to feed a percarboxylic acid to the water, and a first measuring device which is configured to measure the concentration of phosphorus in the water and generate output data relating to the measured concentration of the phosphorus, wherein the apparatus is constructed and arranged to receive the output data relating to the measured concentration of the phosphorus from the first measuring device, monitor the measured concentration of the phosphorous in the water, and to adjust the amount of the agent that is fed into the water by the first dosing device and/or adjust the amount of the percarboxylic acid that is fed to the water by the second dosing device based on the measured concentration of the phosphorus.

The first dosing device may be configured to add or feed a precipitation/ coagulation agent, i.e. the source of ions described above, into the water. The first dosing device may comprise one or more pumps or valves which facilitate delivery of the source of ions, optionally via one or more lines, into the water. The first dosing device may be operated manually or automatically. The source of ions may be added or fed into the water continuously or at regular intervals at a constant rate, or the dosing may be adjusted based on measured concentrations, measured by the first measuring device.

A second dosing device may be configured to add or feed the percarboxylic acid into the water stream. The dosing device may comprise one or more pumps or valves which facilitate delivery of the percarboxylic acid, optionally via one or more lines, into the water. The second dosing device may be operated manually or automatically.

PAA is commercially available as an acidic quaternary equilibrium mixture with acetic acid, hydrogen peroxide (H2O2) and water, as illustrated in reaction (1) below, and accordingly, may be fed into the water in the form of the equilibrium mixture.

CH3COOH + H2O2 CH3CO-OOH + H₂O (1)

Due to the greater instability and faster decomposition times of PF A, PFA may need to be generated immediately before use. Preferably, PFA is generated in situ (i.e. at the site of water treatment). As such, the second dosing device may comprise a reaction vessel in which PFA is produced. In other embodiments, PFA is produced outside the water treatment system and transferred directly and rapidly to the dosing device for feeding to water. A preferred preparation method of PFA comprises mixing formic acid with hydrogen peroxide according to reaction (2) below optionally, in the presence of an acid catalyst such as sulphuric acid, ascorbic acid, or boric acid. The equilibrium of reaction (2) below may be shifted in favour of PFA formation if the molar ratio of formic acid to hydrogen peroxide is increased, or by removing water from the reaction. CHO-OH + H₂O₂ CHO-OOH + H₂O (2)

The percarboxylic acid may be fed into the water continuously (i.e. without pause) or at regular, pre-determined time intervals. The amount of percarboxylic acid fed into the water may be regulated (i.e. adjusted) based on the measured level of phosphorus (and optionally also TSS) in the water and further optionally also the measured level of residual percarboxylic acid. As indicated above, the level of residual percarboxylic acid in water provides an indicator of disinfection efficacy.

In some examples, the feeding of the percarboxylic acid into the water is automated. In these examples, and with further reference to Figure 3, the control apparatus (18) described above may be operatively connected to the percarboxylic acid dosing device (14). The control apparatus (18) may be constructed and arranged to receive output data from the first measuring device (19) relating to the concentration of phosphorus in the water, and to regulate the feeding of the percarboxylic acid from the second dosing device (14) to the water based on such output data. This may ensure that the impact of any change in the concentration of phosphorus on the disinfection performance of the percarboxylic acid is minimised or negated by an adjustment in the amount of percarboxylic acid that is fed to the water for disinfection.

Thus, based on output data received from the first measuring device (11), the control apparatus (18) may detect an increase in the concentration of phosphorus above a pre-defined threshold concentration, and cause the second dosing device (14) to increase the amount of percarboxylic acid that is fed to the water to be treated over a given period until the concentration of phosphorus is restored to the pre-defined threshold. This may be effected, for example, by increasing the velocity of a pump or opening of a valve which facilitates delivery of the percarboxylic acid from the second dosing device (14) to the water to be treated. Conversely, based on output data received from the first measuring device (11), the control apparatus (18) may detect a decrease in concentration of phosphorus below the pre-defined threshold value and cause the second dosing device (14) to decrease the amount of percarboxylic acid that is fed to the water to be treated over a given period of time to avoid unnecessary depletion of the percarboxylic acid and an increase in residual percarboxylic acid concentration above regulatory limits. This may be effected, for example, by decreasing the velocity a pump or closing of a valve which would otherwise facilitate delivery of the percarboxylic acid from the second dosing device (14) to the water to be treated.

An appropriate computer program code (34), as executed by the processor (28) and stored in memory (29) as described above, may determine, based on output measurement data received from the first measuring device (11), whether the measured concentration of phosphorus is above or below the pre-defined threshold, and the adjustment required in the amount of the percarboxylic acid fed to the water to be treated, as described herein. Accordingly, the control apparatus (18) may be constructed and arranged to compare the measured concentration of phosphorus with the pre-defined threshold phosphorus/phosphate concentration, and may be constructed and arranged to adjust the performance of the second dosing device (14).

In further examples, the dosing of the percarboxylic acid may additionally or alternatively be adjusted based on the concentration of residual percarboxylic acid. In these examples, a second measuring device (12) may be provided to measure the residual concentration of the percarboxylic acid. The control apparatus (18) may be constructed and arranged to receive output data from the second measuring device (12) relating to the concentration of the residual percarboxylic acid and to regulate the feeding of the percarboxylic acid from the second dosing device (14) to the water based on such output data. Thus, for example, based on output data received from the second measuring device (12), the control apparatus (18) may detect an increase in concentration of residual percarboxylic acid above a pre-defined threshold concentration, and cause the second dosing device (14) to decrease the amount of percarboxylic acid that is fed to the water to be treated over a given period to avoid unnecessary depletion of the percarboxylic acid and an increase in residual percarboxylic acid concentration above regulatory limits, and to restore the concentration of residual percarboxylic acid to the pre-defined threshold. This may be effected, for example, by decreasing the velocity of a pump or closing a valve which otherwise facilitate delivery of the percarboxylic acid from the second dosing device (14) to the water to be treated. Conversely, based on output data received from the second measuring device (12), the control apparatus (18) may detect a decrease in concentration of residual percarboxylic acid to below the pre-defined threshold value and cause the second dosing device (14) to increase the amount of percarboxylic acid that is fed to the water to be treated over a given period of time to maintain the required disinfection efficacy. This may be effected, for example, by increasing the velocity of a pump or opening a valve which facilitates delivery of the percarboxylic acid from the second dosing device (14) to the water to be treated. In examples where the percarboxylic acid is synthesised in situ, changes in the dosing of percarboxylic acid may be effected by corresponding changes in the rate of production of percarboxylic acid (e.g. by changing the amount of reactants available to produce the percarboxylic acid).

The pre-defined threshold concentration of residual percarboxylic acid may be determined based on relevant regulatory limits governing the area in which the water treatment system is located. In some embodiments, the pre-defined threshold concentration of PFA may be from 0.1 mg/1 to 2 mg/1, 0.1 mg/1 to 1 mg/1, or from 0.2 mg/1 to 0.8 mg/1. In some embodiments, the pre-defined threshold concentration of PAA may be from 0.4 mg/1 to 8 mg/1, 0.4 mg/1 to 4 mg/1, or from 1.6 mg/1 to 3.2 mg/1

In some embodiments, the method of treating water of the invention is a continuous method. In an example of the invention, a PFA solution is contacted with the water at a basal concentration (i.e. the concentration of PFA at the point of addition to water before its consumption) of from 0.1 to 3 mg/1, or from 0.2 to 2 mg/1, 0.3 to 1.5 mg/1, or from 0.3 to 1 mg/1, based on the amount of active PFA. In another example of the invention, a PAA solution is contacted with the water at a basal concentration (i.e. the concentration of PAA at the point of addition to water before its consumption) of from 0.4 to 12 mg/1, or from 0.8 to 8 mg/1, 1.2 to 6.0 mg/1, or from 1.2 to 4 mg/1, based on the amount of active PAA. The percarboxylic acid may be continually fed from the second dosing device (14) in which it may be produced, to the water to be treated, at the above active concentrations. In response to changes in concentrations of phosphorus and/or changes in residual percarboxylic acid concentration, the dosing of the percarboxylic acid may be adjusted as described above.

A PID controller as referred to previously, may continuously calculate an error value as the difference between the pre-defined set concentration of residual percarboxylic acid and the measured concentration of percarboxylic acid, and may subsequently apply a correction based on proportional, integral, and derivative terms. The controller may attempt to minimize the error over time by adjustment of its output (for example, by adjustment of the velocity of a pump delivering the percarboxylic acid) such that that the concentration of the percarboxylic acid does not exceed the pre-defined threshold concentration.

Measurement of percarboxylic acid

In the method for treating water according to the present invention, the level of residual percarboxylic acid may preferably be measured and monitored continuously and in real-time in order to detect any fluctuations from a threshold concentration of residual PF A. In this context, by “continuously” it is meant that the level of percarboxylic acid is measured at regular, repeating intervals without interruption. For example, the level of residual percarboxylic acid may be measured and monitored at regular intervals such as every 2 minutes, every 3 minutes, every 4 minutes, every 5 minutes, every 10 minutes, every 30 minutes or every hour. The measurements may be performed online or inline.

The percarboxylic acid may be measured manually or in an automated fashion. The percarboxylic acid may be measured using standard methods including amperometric techniques and colorimetric methods such as the well-established DPD (N,N-diethyl-p-phenylenediamine) method. DPD kits and photometers are commercially available. Examples of DPD analysers which may be used for percarboxylic acid measurements include Hach® CL- 17 analyser, Hach® CL-17sc analyser, or a Xylem® 3017M analyser. The percarboxylic acid may also be measured using a standard Reflectoquant Peracetic acid test.

The level of residual percarboxylic acid may be measured by the second measuring device (14) at any process location after the percarboxylic acid is fed into the water. Preferably, the measurement is commenced after a sufficient contact time (i.e. time between addition of percarboxylic acid to water and measurement) has elapsed. A contact time of at least 5 minutes, 10 minutes, 20 minutes or 30 minutes is desirable. In some examples, a contact time of at least one hour or two hours is provided. In a continuously flowing system, this means that measurement is performed at a flowing distance of at least 1 minute, at least 5 minutes, 10 minutes, 20 minutes, 30 minutes, one hour or two hours downstream of the point at which the percarboxylic acid is fed into the water. Although at least some aspects of the embodiments described herein with reference to the drawings comprise computer processes performed in processing systems or processors, the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of non-transitory source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other non-transitory form suitable for use in the implementation of processes according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a solid-state drive (SSD) or other semiconductor-based RAM; a ROM, for example a CD ROM or a semiconductor ROM; a magnetic recording medium, for example a floppy disk or hard disk; optical memory devices in general; etc.

Use

Also provided by the present invention is the use of a phosphorus precipitation and/or coagulation agent to reduce the amount of a percarboxylic acid required to disinfect water comprising at least one microorganism, wherein the water further comprises a concentration of phosphorus present as inorganic phosphates and/or as organic phosphorus, and wherein the use comprises reducing the concentration of the phosphorus in the water by contacting the water with the precipitation and/or coagulation agent to precipitate and/or coagulate the phosphorus and separating the precipitate and/or coagulate from the water.

In particular, the phosphorus precipitation/coagulation agent can be a source of calcium, iron, aluminium, or rare earth metal ions which can be used to form phosphorus precipitation and/or phosphorus coagulates. Preferably the agent is a source of iron and/or aluminium ions. The agent may be used as in any of the methods described herein.

The following are intended as examples only and do not limit the present disclosure. 1 EXAMPLES

Example 1

The efficacy of performic acid (PF A) was tested in wastewater with different concentrations of total suspended solids (TSS) and phosphorus (comprising inorganic phosphates and organic phosphorus).

Purified waste water from a Finnish waste water treatment plant was used, and dirty incoming waste water and or sludge from the plant in question was added into the water in order to adjust TSS and phosphorus concentrations to desired levels (as shown in the table below).

Phosphorus was measured using two methods. Phosphates present in the sample (reactive orthophosphate, PO4³ ) were measured using commercially available USEPA PhosVer 3 method (number 8048) from Hach according to manufacturer’s instructions. The values determined represent “Free phosphates” in the sample. It is noted in general that phosphorus concentration is approximately one third of phosphate concentration, and therefore the concentrations measured were divided by three to obtain the “Free phosphates as phosphorus” values shown in the table below.

Total phosphorus was measured as phosphate using another method from Hach, USEPA PhosVer 3 with acid persulfate digestion method (number 8190). This method converts organic phosphorus to phosphate (such that all phosphorus in the sample is present as phosphate) and then the amount of phosphate present is measured. The concentrations of phosphate determined by this method were also divided by 3 in order to obtain the phosphorus concentrations shown in the table below.

Total suspended solids (TSS) was measured as follows: 100 - 200 ml sample was filtrated through a weighted glass fiber filter with pore size 1.6pm. The solid material and the filter were dried at +105 °C for 2 h. The filter was weighted and the TSS content calculated based on the sample volume and the weight of material on the filter. Also, Escherichia coli cells (grown overnight on agar-plate and suspended in 0.9% NaCl solution) were added into the water in order to ensure that the bacterial counts were in the range 1000000- 2000000 cfu/ml (total bacteria) and 100000 to 700000 cfu/ml (E.coli).

0, 0.5, 1, 2 or 4 mg/1 PFA was added into the test water, and after 15 min contact time the surviving cells were enumerated using Total aerobic count petrifilms (3M) and Compact dry EC (Nissui Pharma Solutions). Bacteria were cultivated overnight at +37°C and results were calculated.

Results are shown in Table 1 below and in Figures 1 and 2.

Table 1 - Efficacy of performic acid (PFA)

As can be seen from Figure 1 and Figure 2, when the levels of phosphorus and TSS are higher a greater amount of PFA is required in order to achieve an efficient disinfection (i.e. reduction of bacterial cell counts to acceptable levels).

The present invention also provides the following aspects and embodiments:

1. A disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising:

(i) treating the water to reduce phosphorus to a concentration of 0.7 mg/1 or less; and (ii) contacting the water treated in (i) with an amount of percarboxylic acid to provide the disinfection.

2. The method of clause 1, wherein (i) comprises treating the water to reduce the concentration of total suspended solids.

3. The method of clause 1 or clause 2, wherein the amount of percarboxylic acid is controlled based on the concentration of phosphorus in the treated water after (i), and optionally also the concentration of total suspended solids in the treated water.

4. The method of any of clauses 1 to 3, comprising measuring the concentration of phosphorus in the water prior to (i) and/or after (i).

5. The method of any of clauses 1 to 4, comprising measuring the concentration of total suspended solids in the water.

6. The method of clause 4 or clause 5, wherein measuring the concentration of phosphorus occurs at least once an hour to at least once a week, and preferably wherein the measuring occurs at least once a day.

7. The method of any of clauses 4 to 6, wherein measuring the concentration of total suspended solids occurs at least once every half an hour to at least once a week, and preferably wherein the measuring occurs at least once every half an hour.

8. The method of any of clauses 4 to 7, comprising modifying a rate of addition of the percarboxylic acid to the water based on the measured concentration of phosphorus, and optionally based on the measured concentration of total suspended solids.

9. The method of any of clauses 1 to 8, wherein treating the water to reduce the concentration of phosphorus comprises treating the water to achieve precipitation, coagulation, biological removal and/or physical removal of phosphorus, preferably wherein the treating comprises contacting the water with an agent that is a precipitation and/or coagulation agent to form a phosphorus precipitate and/or coagulate, and removing the precipitate and/or coagulate with sedimentation and/or filtration.

10. The method of clause 9, wherein the water is contacted with a precipitation and/or coagulation agent that is a source of calcium, iron, aluminium or rare earth ions, and preferably a source of iron and/or aluminium ions. 11. The method of any of clauses 1 to 10, wherein treating the water to reduce the concentration of phosphorus comprises using microorganisms to assimilate or remove phosphorus from the water.

12. The method of any of clauses 2 to 11 , wherein treating the water to reduce the concentration of total suspended solids comprises one or more of screening, agglomeration, sedimentation, biofiltration, and treatment in an oxidation pond.

13. The method of any of clauses 1 to 12, wherein the percarboxy lie acid comprises performic acid and/or peracetic acid, and preferably wherein the percarboxylic acid is performic acid.

14. The method of any of clauses 1 to 13, wherein the concentration of phosphorus is reduced to 0.5 mg/1 or less, preferably 0.3 mg/1 or less, more preferably 0.1 mg/1 or less prior to contacting the water with the amount of percarboxylic acid.

15. The method of any of clauses 2 to 14, wherein the concentration of the total suspended solids is reduced to 20 mg/1 or less, preferably 10 mg/1 or less prior to contacting the water with the amount of percarboxy lie acid.

16. The method of any of clauses 1 to 15, wherein the percarboxy lie acid is performic acid and the performic acid is contacted with the water in an amount of from 0.1 to 2 mg/1, preferably 0.1 mg/1 to 1.5 mg/1, more preferably 0.2 to 1.0 mg/1.

17. The method of any of clauses 1 to 16, wherein the water comprises wastewater, and preferably wherein the method comprises performing primary treatment and/or secondary treatment of the wastewater.

18. The method of clause 17, comprising treating an influent of secondary sedimentation to reduce (a) the concentration of phosphorus in the water and/or (b) the amount of total suspended solids in the water, prior to contacting the water with the amount of percarboxylic acid.

19. The method of clause 18, comprising contacting the influent of secondary sedimentation with a source of iron ions simultaneously or subsequent to aeration of the influent to form a phosphorus precipitate, and removing the precipitate with sedimentation and/or filtration.

20. The method of any of clauses 17 to 19, wherein the method further comprises performing tertiary treatment of the wastewater, optionally wherein:

(a) the tertiary treatment comprises contacting the wastewater with a source of iron ions to form a phosphorus precipitate, and removing the precipitate with sedimentation and/or filtration; or (b) using the percarboxylic acid to provide the disinfection is performed during tertiary treatment.

21. A disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising contacting the water with an amount of percarboxylic acid to provide the disinfection, wherein the amount of percarboxylic acid is controlled based on the concentration of phosphorus in the water, and optionally also the concentration of total suspended solids in the water.

22. The method of clause 21, comprising treating the water to reduce (a) the concentration of phosphorus in the water, and optionally (b) the concentration of total suspended solids in the water, prior to contacting the water with the amount of percarboxylic acid.

23. The method of clause 21 or clause 22, comprising measuring the concentration of phosphorus in the water before contacting the water with the amount percarboxylic acid.

24. The method of any of clauses 21 to 23, comprising measuring the concentration of total suspended solids in the water before contacting the water with the amount percarboxylic acid.

25. The method of clause 23 or clause 24, wherein measuring the concentration of phosphorus occurs at least once an hour to at least once a week, and preferably wherein the measuring occurs at least once a day.

26. The method of any of clauses 23 to 25, wherein measuring the concentration of total suspended solids occurs at least once every half an hour to at least once a week, and preferably wherein the measuring occurs at least once every half an hour.

27. The method of any of clauses 23 to 26, comprising modifying a rate of addition of the percarboxylic acid to the water based on the measured concentration of phosphorus, and optionally based on the measured concentration of total suspended solids.

28. The method of any of clauses 22 to 27, wherein treating the water to reduce the concentration of phosphorus comprises treating the water to achieve precipitation, coagulation, biological removal and/or physical removal of phosphorus, preferably wherein the treating comprises contacting the water with an agent that is a precipitation and/or coagulation agent to form a phosphorus precipitate and/or coagulate, and removing the precipitate and/or coagulate with sedimentation and/or filtration. 29. The method of clause 28, wherein the water is contacted with a precipitation and/or coagulation agent that is a source of calcium, iron, aluminium or rare earth ions, and preferably a source of iron and/or aluminium ions.

30. The method of any of clauses 22 to 29, wherein treating the water to reduce the concentration of phosphorus comprises using microorganisms to assimilate or remove phosphorus from the water.

31. The method of any of clauses 22 to 30, wherein treating the water to reduce the concentration of total suspended solids comprises one or more of screening, agglomeration, sedimentation, biofiltration, and treatment in an oxidation pond.

32. The method of any of clauses 21 to 31, wherein the percarboxylic acid comprises performic acid and/or peracetic acid, and preferably wherein the percarboxylic acid is performic acid.

33. The method of any of clauses 22 to 32, wherein the concentration of phosphorus is reduced to 0.7 mg/1 or less, 0.5 mg/1 or less, preferably 0.3 mg/1 or less, more preferably 0.1 mg/1 or less prior to contacting the water with the amount of percarboxylic acid.

34. The method of any of clauses 22 to 33, wherein the concentration of the total suspended solids is reduced to 20 mg/1 or less, preferably 10 mg/1 or less prior to contacting the water with the amount of percarboxy lie acid.

35. The method of any of clauses 21 to 34, wherein the percarboxylic acid is performic acid and the performic acid is contacted with the water in an amount of from 0.1 to 2 mg/1, preferably 0.1 mg/1 to 1.5 mg/1, more preferably 0.2 to 1.0 mg/1.

36. The method of any of clauses 21 to 35, wherein the water comprises wastewater, and preferably wherein the method comprises performing primary treatment and/or secondary treatment of the wastewater.

37. The method of clause 36, comprising treating an influent of secondary sedimentation to reduce (a) the concentration of phosphorus in the water and/or (b) the amount of total suspended solids in the water, prior to contacting the water with the amount of percarboxylic acid.

38. The method of clause 37, comprising contacting the influent of secondary sedimentation with a source of iron ions simultaneously or subsequent to aeration of the influent to form a phosphorus precipitate, and removing the precipitate with sedimentation and/or filtration.

39. The method of any of clauses 36 to 38, wherein the method further comprises performing tertiary treatment of the wastewater, optionally wherein: (a) the tertiary treatment comprises contacting the wastewater with a source of iron ions to form a phosphorus precipitate, and removing the precipitate with sedimentation and/or filtration; or

(b) using the percarboxylic acid to provide the disinfection is performed during tertiary treatment. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the method of any of clauses 1 to 39. A water treatment system comprising the apparatus of clause 40, the system comprising: a first dosing device which is configured to feed into the water an agent that is a precipitation and/or coagulation agent to form a phosphorus precipitate and/or coagulate, a second dosing device which is configured to feed a percarboxylic acid to the water, and a first measuring device which is configured to measure the concentration of phosphorus in the water and generate output data relating to the measured concentration of the phosphorus, wherein the apparatus is constructed and arranged to receive the output data relating to the measured concentration of the phosphorus from the first measuring device, monitor the measured level of the phosphorous in the water, and to adjust the amount of the agent that is fed into the water by the first dosing device and/or adjust the amount of the percarboxylic acid that is fed to the water by the second dosing device based on the measured concentration of the phosphorus. The system of clause 41, wherein the system further comprises: a second measuring device which is configured to measure the concentration of percarboxylic acid in the water and generate output data relating to the measured concentration of percarboxylic acid, and wherein the apparatus is constructed and arranged to receive the output data relating to the measured concentration of the percarboxylic acid from the second measuring device, monitor the measured concentration of the percarboxylic acid in the water, and adjust the amount of the percarboxylic acid that is fed to the water by the second dosing device based on the measured concentration of the percarboxylic acid.

43. Use of phosphorus precipitation and/or coagulation agent to reduce the amount of a percarboxylic acid required to disinfect water comprising at least one microorganism, wherein the water further comprises a concentration of phosphorus present as inorganic phosphates and/or as organic phosphorus, and wherein the use comprises reducing the concentration of the phosphorus in the water by contacting the water with the precipitation and/or coagulation agent to precipitate and/or coagulate the phosphorus and separating the precipitate and/or coagulate from the water.

44. The use of clause 43, wherein the use is as defined in any of clauses 1 to 39.

Other variants or use cases of the disclosed techniques may become apparent to the person skilled in the art once given the disclosure herein. The disclosure is not limited by the described embodiments but only by the accompanying claims.

Claims

2. The method of claim 1, wherein (i) comprises treating the water to reduce the concentration of total suspended solids.

3. The method of claim 1 or claim 2, wherein the amount of percarboxylic acid is controlled based on the concentration of phosphorus in the treated water after (i), and optionally also the concentration of total suspended solids in the treated water.

4. The method of any of claims 1 to 3 comprising:

(a) measuring the concentration of phosphorus in the water prior to (i) and/or after (i); and/or

(b) measuring the concentration of total suspended solids in the water.

5. A disinfection method for water comprising at least one microorganism and phosphorus present as inorganic phosphates and/or as organic phosphorus, the method comprising contacting the water with an amount of percarboxylic acid to provide the disinfection, wherein the amount of percarboxylic acid is controlled based on the concentration of phosphorus in the water, and optionally also the concentration of total suspended solids in the water.

6. The method of claim 5, comprising treating the water to reduce (a) the concentration of phosphorus in the water, and optionally (b) the concentration of total suspended solids in the water, prior to contacting the water with the amount of percarboxylic acid.

7. The method of claim 5 or claim 6, comprising: (a) measuring the concentration of phosphorus in the water before contacting the water with the amount percarboxylic acid; and/or

(b) measuring the concentration of total suspended solids in the water before contacting the water with the amount percarboxy lie acid.

8. The method of claim 4 or claim 7, wherein:

(a) measuring the concentration of phosphorus occurs at least once an hour to at least once a week, and preferably wherein the measuring occurs at least once a day; and/or

(b) measuring the concentration of total suspended solids occurs at least once every half an hour to at least once a week, and preferably wherein the measuring occurs at least once every half an hour.

9. The method of claim 4, claim 7, or claim 8, comprising modifying a rate of addition of the percarboxylic acid to the water based on the measured concentration of phosphorus, and optionally based on the measured concentration of total suspended solids.

10. The method of any of claims 1 to 4 or 6 to 9, wherein treating the water to reduce the concentration of phosphorus comprises treating the water to achieve precipitation, coagulation, biological removal and/or physical removal of phosphorus, preferably wherein the treating comprises contacting the water with an agent that is a precipitation and/or coagulation agent to form a phosphorus precipitate and/or coagulate, and removing the precipitate and/or coagulate with sedimentation and/or filtration.

11. The method of claim 10, wherein the water is contacted with a precipitation and/or coagulation agent that is a source of calcium, iron, aluminium or rare earth ions, and preferably a source of iron and/or aluminium ions.

12. The method of any of claims 1 to 4 or 6 to 11, wherein treating the water to reduce the concentration of phosphorus comprises using microorganisms to assimilate or remove phosphorus from the water.

13. The method of any of claims 1 to 4 or 6 to 12, wherein treating the water to reduce the concentration of total suspended solids comprises one or more of screening, agglomeration, sedimentation, biofiltration, and treatment in an oxidation pond.

14. The method of any of claims 1 to 13, wherein the percarboxylic acid comprises performic acid and/or peracetic acid, and preferably wherein the percarboxylic acid is performic acid.

15. The method of any of claims 1 to 4 or 6 to 14, wherein:

(a) the concentration of phosphorus is reduced to 0.7 mg/1 or less, 0.5 mg/1 or less, preferably 0.3 mg/1 or less, more preferably 0.1 mg/1 or less prior to contacting the water with the amount of percarboxylic acid; and/or

(b) the concentration of the total suspended solids is reduced to 20 mg/1 or less, preferably 10 mg/1 or less prior to contacting the water with the amount of percarboxylic acid.

16. The method of any of claims 1 to 15, wherein the percarboxylic acid is performic acid and the performic acid is contacted with the water in an amount of from 0.1 to 2 mg/1, preferably 0.1 mg/1 to 1.5 mg/1, more preferably 0.2 to 1.0 mg/1.

17. The method of any of claims 1 to 16, wherein the water comprises wastewater, and preferably wherein the method comprises performing primary treatment and/or secondary treatment of the wastewater.

18. The method of claim 17, comprising treating an influent of secondary sedimentation to reduce (a) the concentration of phosphorus in the water and/or (b) the amount of total suspended solids in the water, prior to contacting the water with the amount of percarboxylic acid.

19. The method of claim 18, comprising contacting the influent of secondary sedimentation with a source of iron ions simultaneously or subsequent to aeration of the influent to form a phosphorus precipitate, and removing the precipitate with sedimentation and/or filtration.

20. The method of any of claims 17 to 19, wherein the method further comprises performing tertiary treatment of the wastewater, optionally wherein:

(a) the tertiary treatment comprises contacting the wastewater with a source of iron ions to form a phosphorus precipitate, and removing the precipitate with sedimentation and/or filtration; or

(b) using the percarboxylic acid to provide the disinfection is performed during tertiary treatment.

21. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the method of any of claims 1 to 20.

22. A water treatment system comprising the apparatus of claim 21, the system comprising: a first dosing device which is configured to feed into the water an agent that is a precipitation and/or coagulation agent to form a phosphorus precipitate and/or coagulate, a second dosing device which is configured to feed a percarboxylic acid to the water, and a first measuring device which is configured to measure the concentration of phosphorus in the water and generate output data relating to the measured concentration of the phosphorus, wherein the apparatus is constructed and arranged to receive the output data relating to the measured concentration of the phosphorus from the first measuring device, monitor the measured level of the phosphorous in the water, and to adjust the amount of the agent that is fed into the water by the first dosing device and/or adjust the amount of the percarboxylic acid that is fed to the water by the second dosing device based on the measured concentration of the phosphorus.

23. The system of claim 22, wherein the system further comprises: a second measuring device which is configured to measure the concentration of percarboxylic acid in the water and generate output data relating to the measured concentration of percarboxylic acid, and wherein the apparatus is constructed and arranged to receive the output data relating to the measured concentration of the percarboxylic acid from the second measuring device, monitor the measured concentration of the percarboxylic acid in the water, and adjust the amount of the percarboxylic acid that is fed to the water by the second dosing device based on the measured concentration of the percarboxylic acid.

24. Use of phosphorus precipitation and/or coagulation agent to reduce the amount of a percarboxylic acid required to disinfect water comprising at least one microorganism, wherein the water further comprises a concentration of phosphorus present as inorganic phosphates and/or as organic phosphorus, and wherein the use comprises reducing the concentration of the phosphorus in the water by contacting the water with the precipitation and/or coagulation agent to precipitate and/or coagulate the phosphorus and separating the precipitate and/or coagulate from the water.

25. The use of claim 24, wherein the use is as defined in any of claims 1 to 20.