NZ539117A - Improved effluent treatment for meat industry using dissolved air flotation in series - Google Patents

Abstract

Disclosed herein is a method of wastewater treatment including the following steps: (a) treating the wastewater in a first acid phase dissolved air flotation (DAF) unit at a pH above the level that results in substantial splitting of haemoglobin, together with a suitable polymer flocculating agent; (b) removing the flocculated components; (c) treating the wastewater from step (b) in a second alkaline phase DAF unit at a pH above about pH 9.0, together with a suitable polymer flocculating agent; and (d) removing the flocculated components. The method of wastewater treatment particularly includes the steps of: (a) treating the wastewater in a first acid phase DAF unit, together with an inverse emulsion polymer flocculating agent, wherein the pH is between 3.0 and 4.5; (b) removing the flocculated components; (c) treating the wastewater from step (b) in a second alkaline DAF unit at a pH between about 9.0 and about 11.5 together with a cationic polymer flocculating agent; and (d) removing the flocculated component. This method of wastewater treatment is particularly suitable for treating wastewater from a meat processing industry.

Description

)r7 PATENTS FORM NO. 5 Our ref: TJ506157NZPR NEW ZEALAND PATENTS ACT 1953 Complete After Provisional No. 539117 Filed 31 March 2005 WASTEWATER TREATMENT We, PATTLE DELAMORE PARTNERS LIMITED a New Zealand Company of Level 4, 235 Broadway, Newmarket, Auckland, New Zealand, hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: 300542258:T J506157NZPR 2 WASTEWATER TREATMENT Technical Field The present invention relates to wastewater treatment. The invention is particularly useful in the improved treatment of meat processing industry wastewater comprising of solids, organic matter, nutrients, namely proteins, and phosphorus and microbial contaminants.

Background Art Dissolved air flotation (DAF) has gained widespread usage for the removal of suspended solids (TSS), oil and grease (O&G), and biochemical oxygen demand (BOD) from meat processing wastewater.

DAF is a unit operation for the removal of suspended solids from water in which the suspended solid particles are lifted up out of the water with micro-bubbles attached to them. These bubbles, usually with a diameter of less than about 100 microns, are created by means of high-pressure water containing a saturated amount of dissolved air collectively known as whitewater. This high pressure water is fed into the front of the 20 flotation space in a DAF tank. When the high-pressure water encounters the effluent atmospheric pressure in the tank, the excess air is released as micro-bubbles that attach to suspended particles, causing them to float to the surface. The high pressure water is normally 15-30% of the amount of water to be treated by DAF. The floated materials are physically removed from the water using scrapers or overflow weirs, while the treated 25 water passes out through collection devices installed in the bottom of the DAF tank. Sulfuric acid and/or bentonite are generally utilised for protein coagulation and precipitation in the meat industry, and cationic polymers are utilised for flocculation of the precipitate to assist in the removal of sludge as float.

Object of the Invention It is an object of the invention to provide an improved method for treatment of wastewater or at least to provide the public with a useful choice. 300542258TJ506157NZPR Summary of the Invention In a first aspect the invention provides a method of wastewater treatment including the 5 following steps: (a) treating the wastewater in a first acid phase DAF unit at a pH above the level that results in substantial splitting of heamoglobin, together with a suitable polymer flocculating agent; (b) removing the flocculated components; (c) treating the wastewater from step (b) in a second alkaline phase DAF unit at a pH above about pH 9.0, together with a suitable polymer flocculating agent; and (d) removing the flocculated components.

Preferably the wastewater from step (b) is collected prior to the alkaline phase.

Preferably the pH of the acid phase is held between about 3.0 and about 4.5.

Preferably the pH of the alkaline phase is held above about 9.0 and more preferably above about 9.5.

Preferably the pH of the alkaline phase is below about 11.5 and more preferably below about 11.0.

Preferably the acid in the acid phase is sulfuric acid.

Preferably the alkali in the alkaline phase is hydrated lime.

Preferably the polymer flocculating agent in the acid phase is an inverse emulsion polymer or an anionic polymer.

Preferably the polymer flocculating agent in the alkaline phase is a cationic polymer.

Preferably the polymer flocculating agent in the alkaline phase is a high molecular weight anionic polymer.

Preferably the method further includes the use of bentonite as an additional flocculating 300542258:TJ506157NZPR 4 agent.

Preferably the level of dissolved reactive phosphorus following wastewater treatment is below 1 g/m3.

Preferably the method further includes the use of a microbial disinfection treatment step after the alkaline DAF phase.

Preferably the method further includes screening the wastewater before entry to the acid 10 phase DAF unit.

^ Preferably step (b) removes solids and ions that compete with phosphorus ions.

In another aspect the invention provides a method of wastewater treatment including the 15 steps of: (a) treating the wastewater in a first acid phase DAF unit, together with an inverse emulsion polymer flocculating agent, wherein the pH is between 3.0 and 4.5; (b) removing the flocculated components; (c) treating the wastewater from step (b) in a second alkaline DAF unit at a pH between about 9.0 and about 11.5 together with a polymer flocculating agent; and (d) removing the flocculated component.

Preferably the acid in the acid phase is sulfuric acid and the alkali in the alkaline phase is hydrated lime.

Preferably an inverse emulsion polymer flocculating agent is also used in the alkaline 30 phase.

Preferably the acid phase pH is kept between 3.5 and 4.5.

Preferably the acid phase is between 9.5 and 11.5.

Preferably the wastewater is screened before entering the acid phase DAF unit. 300542258:TJ506157NZPR Preferably the wastewater is disinfected after step (d).

Figures In order that the invention may be more readily understood, a preferred embodiment of the invention is referred to in the accompanying drawing in which: Figure 1 is a process schematic drawing of the DAF units placed in series showing the general arrangement of the process control units in accordance with the invention. ^10 Figure 2 is a summary of contaminant removal in Pilot Plant Trials.

Detailed Description Although there is prior use of DAF systems to remove pollutants from wastewater, the 15 inventors have surprisingly found that the removal efficiency of the pollutants increases using DAF treatment units in series under certain process conditions. In particular, removal of dissolved phosphorus contaminants from the wastewater is achieved.

The present invention therefore provides a method of treating wastewater and controlling several pollutants, including organic matter, oil and grease, suspended solids, nitrogen, 20 phosphorus and microbial contaminants.

The present invention, in addition, provides a method of improving the physical properties of wastewater, such as clarity of effluent, to allow efficient disinfection of the final discharge using other conventional methods, like ultraviolet disinfection, prior to final discharge of treated effluent to the receiving environment.

The wastewater treatment system uses of off-the-shelf process units, but the placement of the units and the process design to operate the system, is unique and offers unexpected advantages. The use of DAF (Dissolved Air Floatation) units in an acid/alkaline phase series with the removal of flocculated components after the acid phase, without substantial haemoglobin breakdown, is a new concept and has not been tried before to reduce pollutants from wastewater, particularly in the meat industry. The technology would apply to other industries that have wastewater contaminants similar to the meat industry. 300542258:T J506157NZPR The preferred process sequence is in two-stages. In the first stage, biochemical oxygen demand (BOD), oil and grease, nitrogen and suspended solids are primarily removed. In the second stage phosphorus and microbial contaminants are primarily removed. With the combined system, a larger proportion of the contaminants in the wastewater are 5 removed achieving much greater removal efficiencies.

The final wastewater discharge from the treatment process has surprising clarity and is substantially devoid of any haze in the effluent. As a result, additional microbial disinfection using ultraviolet can then be used with enhanced effect.

With reference to Figure 1, a schematic diagram of a preferred arrangement of DAF units ^ in series to treat wastewater is shown with reference to Figure 1.

The input wastewater (influent) is first treated via milli-screening before entry into an equalisation tank to allow uniform discharge of the screened wastewater into the series of DAF units. Alternative screening or filtration options as would be known to a skilled 15 person could also be used, such as Baleen filters. The material that is removed at the screening stage is then transferred to a screenings bin for later solids handling and disposal.

As can be seen in Figure 1, the DAF units are arranged in two phases, the first being an acid phase and the second being an alkaline phase.

The acid phase will preferably be run at a pH below about 4.5 to precipitate proteins, blood colour, and remove alkalinity buffering. The most common acid utilised is sulfuric acid generally operating in a pH range above that at which haemoglobin splits into component parts - haem and globin (preferably between 3.0 - 4.5 pH units). The pH is 25 controlled through automatic pH control systems as would be known to a person skilled in this art. The reduction in pH by the release of hydrogen ions in the acid forces the reduction in alkalinity and also encourages protein precipitation. Other acids can be utilised, for example hydrochloric acid, however in meat industry applications, sulfuric acid is mostly used. Hydrochloric acid is very corrosive and would not be preferred as it is 30 substantially more expensive than sulfuric acid. However, other acids may be used (for example, nitric acid, phosphoric acid) so long as the acids in themselves do not adversely impact on the contaminant load. For example, nitric acid would increase nitrogen levels, and phosphoric acid would increase phosphorus levels prior to the alkaline phase. Use of alkali treatment would be able to correct this at the higher pH use (e.g. 11.0-11.5). 300542258:T J506157NZPR 7 The pH levels for the acid phase progressively become more efficient from 4.5 downwards until about pH 3. Below about pH 3, haemoglobin splits increasing the dissolved organic carbon content. It is known to use acid DAF units at pHs sufficient to split the haemoglobin as this can be used for precipitation/flocculation of the result, however the increase in 5 dissolved carbon is then a problem. To avoid this, the pH in the process according to the present invention is kept above the level that will result in haemoglobin splitting and flocculation is achieved via the use of suitable polymer flocculating agents.

The alkaline phase will preferably be run at a pH above about 9.0 and more preferably above about 9.5 to remove phosphorus, and especially dissolved reactive phosphorus, 10 when hydrated lime is utilised as the alkali material. The alkaline phase is controlled by a ^ pH controller controlling the supply of hydrated lime as a solution. Other alkali, like magnesium hydroxide may be utilised, however, hydrated lime is generally utilised as this results in better phosphorus removal. The pH of the alkaline phase is dependent on the extent of phosphorus removal required. If pH is kept below 10.0 but above 9.5 (low-lime 15 treatment), it can achieve dissolved reactive phosphorus (DRP) at around 1.0 g/m3. If the pH is raised to between 11.0 -11.5 (high-lime treatment), then levels well below 1 g/m3 can be achieved. High lime treatment uses more lime and will also require recarbonation treatment to reduce wastewater pH before discharge from the plant.

Some pH adjustments may be required to optimise the precipitation of protein or 20 phosphorus in the acid or alkaline phase if the effluent stream is different to meat processing wastewaters. Such adjustments would be well within the capabilities of a skilled person once in possession of the invention.

While Figure 1 shows the phases being sequential, it is of course possible for the wastewater exiting the acid phase to be held for later treatment in the alkaline phase.

The wastewater exits the equalisation tank and it is then treated with acid and polymer flocculating agent, such as sulfuric acid and proprietary polymer (selected for example, from Ciba® MAGNAFLOC® or ZETAG®) to assist in an acid flocculation step to flocculate the solids in the wastewater. Sulfuric acid is preferably used in the acid phase, although other acids could also be used. Bentonite or a similar flocculating agent, can also be used to assist protein coagulation and precipitation.

Following treatment with acid, and polymer flocculating agent (and optionally bentonite), the wastewater is treated with high-pressure water containing a saturated amount of dissolved air (whitewater) in the first DAF unit. The flocculated components (i.e. precipitate) form as float sludge (carried via the bubbles in the whitewater) which is then 300542258:TJ506157NZPR 8 removed for solid waste handling and disposal. Removal of the float sludge can be via scraping or any other suitable method.

The pH of the acid DAF phase is controlled at a pH above that which will result in haemoglobin splitting. If haemoglobin in the wastewater breaks down to any great extent, 5 this will result in an increase in dissolved organic carbon (and a higher BOD). Preferably the pH is held above about 3.0 and less than about 4.5 using controlled acid pumping systems controlled by a pH controller.

The wastewater then moves to a flash mix tank or similar unit, where it is treated with an alkali, such as hydrated lime and the pH controlled at a level between about 9.0 and about 10 11.5, preferably greater than about 9.5. The wastewater in the alkaline phase is then \ again treated with a suitable polymer flocculating agent (selected for example, from Ciba® MAGNAFLOC® or ZETAG®) and with whitewater in the second alkaline phase DAF unit. Once again, flocculated precipitate is formed and removed as float sludge, and is then further removed for solid waste handling.

The flocculated components (float sludge) created are then removed prior to the alkaline phase. Preferably this will be via a scraping system.

For the alkaline phase, the pH is kept above about pH 9.0. A suitable polymer flocculating agent is again used to assist precipitation/flocculation. Clarity occurs as the phosphorus is precipitated and other contaminants are precipitated with phosphorus removal. Above 20 about pH 9.5 is preferred to maximise phosphorus removal.

. The initial, acid DAF phase removes solids from the wastewater as well as significant amounts of ions that could compete with phosphorus ions in the alkaline phase. These flocculated components are removed from the system as float sludge (e.g. scraped from the surface of the waste water) which is then disposed of. The alkaline phase can 25 therefore remove significant amounts of phosphorus ions (to below about 1 g/m3) due to the impact of previous phase.

The combination of the acid DAF phase pH being kept above the level that would split haemoglobin (preferably above about pH 3.0), the use of polymers to flocculate the protein in the acid phase, the removal of the float sludge created, and then the use of an alkaline 30 DAF phase having a pH kept above about 9.0 (preferably above about 9.5) again with the use of polymers to assist flocculation, results in a very efficient treatment system resulting in wastewater with low levels of dissolved phosphorus.

Polymer flocculating agents of varying ionicity can be used depending on the waste stream 300542258:TJ506157NZPR 9 and/or site conditions. The polymers assist and increase the efficiency of solids coagulation and flocculation.

The most common cationic precipitants used in the treatment of meat processing effluents are iron(lll) salts and aluminium(lll) salts. These ions react with negatively charged 5 proteins leading to coagulation and flocculation.

Previous thinking was that pH needed to be below about 3.5 to become positively charged to allow anionic polymer use. The inventor has found that, with inverse emulsion polymers, the pH does not need to be below 3.5. Thus flocculation can be achieved well above the pH at which haemoglobin splits. Thus the pH does not need to be below 3.5 to 10 allow effective precipitation, reducing acid demand and subsequent lime demand for pH elevation.

In general terms, for meat industry effluent, the following would be a guide to suitable polymers for use in the process: 0 < pH < 3 - protein has positive charge - usually anionic polymer 15 3.5 < 4.5 - protein is isoelectric (no net charge) - usually inverse emulsion polymer pH > 4.5 - protein has negative charge - usually cationic polymer For protein precipitation the ionicity changes from being negatively charged to positively charged between pH 3.5 - 4.5. For phosphorus removal, when lime is used, then all types of polymers can be utilised as there are different cations or anions that can trigger ^^0 flocculation for meat processing effluents. For example, calcium being a cation requiring cationic polymer, whereas phosphate being an anion requiring anionic polymer. For example Magnafloc X135 (inverse emulsion) can be used in both acid and alkali phases; Cytec Superfloc A130 (a high molecular weight anionic polymer) can be used in the alkali phase. Selection of appropriate polymers will depend on the conditions.

As would be known to a person skilled in this art, various suppliers produce a suite of polymers that could be used at the pH levels used in this process under various brands.

The wastewater exiting the alkaline phase DAF unit may then optionally be readjusted to a neutral, or other desired, pH depending on any discharge limitations, before it is discharged into the environment or is subject to further disinfection treatment or 30 alternative treatment (such as ultraviolet disinfection treatment, due to the clarity of the effluent, or the like). 300542258:T J506157NZPR The whitewater used in the process can be added to the DAF units as freshly prepared, virgin whitewater, or could be recycled from the acid phase using traditional air saturators or in-line pump saturation units as would be known to a person skilled in this art. The whitewater may be utilised from alkaline phase, so long as struvite formation does not 5 occur. The DAF units can be purchased as commercially available units or could be self built. They will include associated pumping, pH control, air saturation systems and sludge handling systems as would be standard with such units.

Examples 10 Experimental Set-Up The pilot plant DAF was operated in series with an acid phase first and then an alkaline (lime) phase.

For the experiments a 1,500 L pilot scale Rendertech™ DAF system was used. This pilot plant DAF consisted of a nominal 1,500 L/hr Scanpure™ dissolved air flotation unit 15 with surface scraper mechanism. The pressurised super-saturated air/water dispersion (whitewater) was added at a set rate of 300 L/hr to the end of the static mixer and in the inlet of the flotation from the pressure tank. The water surface area of the pilot plant was 1.44 m2, and therefore the unit provided a surface loading of 0.9 m3/m2/hr including whitewater. The schematic diagram in Figure 1 is of the pilot scale treatment plant 20 set-up.

A flash mixer/coagulator and a reactor vessel for the alkaline phase were retrofitted to the ) pilot plant DAF.. The static mixer (i.e. a pipe flocculator) consists of two parts, a first part for intensive coagulation mixing and a second part for slow flocculation mixing.

Sulfuric acid was added through injection ports in the pipe flocculator as the coagulant 25 during the acid phase, while lime slurry was added in the reactor vessel directly for the alkaline phase. An ionic polymer was directly injected in the pipe flocculator for both phases. Chemical dosage pumps controlled the acid, lime and polymer dosage. The pH in the two different pH control set points (low pH acid condition and high pH alkaline condition) was manually controlled.

The sludge float layer which formed in the DAF units as a result of precipitation was removed using a chain scraper and was collected in the sludge collection trough. During the experimental period the flow into the DAF units was adjusted to an influent feed rate of 1,000 L/hr for both the acid phase and the alkaline phase processes. The flow of whitewater was also maintained at 300 L/hr for both the acid and alkaline phases. 300542258:TJ506157NZPR 11 Feed Source For the experiments the raw effluent consisted of a mixture of screened effluent from an integrated beef and sheep processing plant beef contra shear sump and combined with 5 green effluent collected from ovine gut cutter and rendering plant. The raw effluent streams were collected at the same time as when the trials were run for the acid phase.

For the alkaline phase, the feed source was the treated effluent discharged from the pilot plant during the acid phase. •10 Coagulants and Polymer Used For coagulation during the acid phase, sulfuric acid was added to the raw effluent at a 20% dilution for all runs except the first run, which was run at 10% dilution. The amount of acid consumption depended on whether the trial was run at a set point of 3 pH units or at 4 pH units.

Similarly, the hydrated lime was added during the alkaline phase in slurry at a solution of 20%, except for the first run which was added at a solution of 50%. The amount of lime slurry addition depended on the initial pH of the acid phase effluent and the set point of 9.5 pH units.

The flocculant used in the runs varied. Magnafloc® X135, an inverse emulsion ^p0 polymer, was used in both the acid and alkali phases with excellent results.

Magnafloc® 919, an anionic polymer, was used in the acid phase in conjunction with Cytec Superfloc® A130, a high molecular weight anionic polymer, in the alkaline phase, also with excellent results.

Operating Conditions The pilot scale system was run in two phases. The initial acid phase was run where the effluent was fed and treated to a pH set point of either 3 pH units or 4 pH units. The intermediate stage (acid effluent) was then collected and stored in a truck tanker until about 5,000 L of effluent was collected to enable the start of the alkaline phase test. 30 The alkaline phase was run in the same manner as the acid phase, however, lime was added in a reactor vessel and mixed to reach 9.5 pH units prior to being pumped into the DAF. It would of course be preferable to avoid the need for intermediate stage collection. 300542258:TJ506157NZPR 12 For each phase, the pilot scale DAF was run for at least 1 hour equivalent to hydraulic retention time, prior to any sampling programme. All the pilot scale trials were run in a continuous mode for at least 4 hours in order to provide a steady state operating conditions for the DAF unit and also to enable collection of enough acid phase effluent for the 5 alkaline phase treatment.

The air saturation pressure was maintained above 5 bar on automatic set-point pressure controllers. The whitewater feed rate was manually controlled at 300 L/hr and the main effluent flow feed rate was manually controlled at 1,000 L/hr with valves. The influent was pumped at a higher flow rate than 1,000 L/hr, with valve diversions in place to 10 maintain a set water pressure while diverting the excess flow back into the influent | reservoir. The whitewater saturation vessel was supplied with potable water.

The acid, lime and polymer pumps were controlled using variable speed drives (either on motor control or on speed/stroke control) and the feed rates were maintained to ensure the pH set points were maintained during each run.

The polymer feed rate was held the same for both phases on the assumption that above a certain dosage the polymer was not as critical in forming floes of precipitated proteins or phosphorus for removal by flotation.

The various operating parameters for the pilot plant trials are summarised in Table 1.

Table 1: Operating Parameters for the Pilot Plant Feed Rate Description Acid Phase Alkaline phase Influent (L/hr) 1,000 1,000 Whitewater (L/hr) 300 300 pH set point 3.0 or 4.0 9.5 Sulfuric Acid (kg/m3) 0.21 to 1.4 not applicable Hydrated Lime (kg/m3) not applicable 0.11-0.54 Polymer (mL/m3) 2.1 to 2.4 2.1 to 2.4 For 2 runs, ultraviolet disinfection studies were undertaken. A small ultraviolet disinfection unit (Steriflo 800S (50W UV lamp) - Contamination Control Technologies, Auckland) with a treatment capacity of 1,500 - 2,500 L/hr was set-up to disinfect treated wastewater after the alkaline phase treatment. 300542258:TJ506157NZPR 13 Pilot Plant Results and Analysis Sampling and Analyses There were a total of 15 trial runs for the pilot scale trial of which 15 runs were undertaken 5 to determine DRP removal and 6 runs were undertaken to determine other contaminant removal in addition to DRP. Two runs were also undertaken specifically to determine the removal of microbial contaminants.

The influent, acid phase effluent, stored acidified effluent and alkaline phase final effluent was sampled every 30 minutes as grab samples and collected as a composite 10 sample. All samples were analysed in accordance with Standards Methods (APHA, " 1998) for total suspended solids (TSS), carbonaceous biochemical oxygen demand (CBOD5), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), total phosphorus (TP), total dissolved phosphorus (TDP) and dissolved reactive phosphorus (DRP).

The samples collected for microbial analysis were collected as discrete grab samples at 15 intervals of 60 minutes apart and enumerated for Faecal Conforms and E. Coli. for the raw influent, acid phase effluent, alkaline phase effluent and post-UV treatment effluent. Additional microbial sampling for Giardia and Cryptosporidium were undertaken on 50 L sample of acid phase and alkaline phase effluent passed though micro-filters.

Effluent Characterisation Table 2 shows the variability of the raw effluent contaminants during the trials. 300542258:T J506157NZPR 14 Table 2: Typical Raw Effluent Stream Characteristics Parameter Range Average Biochemical oxygen demand (g/m3) 1,150-3,580 2,248 Soluble biochemical oxygen demand (g/m3) 471 -931 601 Total chemical oxygen demand (g/m3) 2,500-8,180 4,685 Soluble chemical oxygen demand (g/m3) 643-1,440 948 Total Kjeldahl nitrogen (g/m3) 155-249 195 Total ammoniacal nitrogen (g/m3) 19.7-41.0 .3 Total phosphorus (g/m3) 39.9 - 68.1 48.1 Total dissolved phosphorus (g/m3) 33.4-53.1 38.8 Dissolved reactive phosphorus (g/m3) 28.5-45.0 34.5 Faecal Coliform (cfu/100 mL) .2 - 6.9E+06 not applicable E.Coli (cfu/100mL) 3.1 - 4.2E+06 not applicable Chemical Usage Demands The chemical usage demands for each trial were different as a result of the variable 5 nature of the raw effluent during each trial. The polymer usage was fixed at around 2.1 mL/m3 for all trials except minor fluctuations observed in two trials (Trial Runs 8 and 9 at 2.4 mL/m3).

The acid usage was dependant on the initial effluent strength (raw effluent) and the acid phase pH set point. The acid use ranged between 0.2 - 1.4 kg/m3 effluent 10 regardless of the acid phase set point of either 3 or 4 pH units. Whist the variability in ^ the raw effluent stream was expected to a certain extent, it was not anticipated for the large and sudden variations in raw effluent quality that occurred throughout the trials.

The hydrated lime usage was reasonably constant between 198-216 g/m3 effluent treated for trials running at an acid set point 4 pH units. The lime usage when the acid phase 15 was at 3 pH units was between 180 - 336 g/m3 except for the first trial that showed the lime usage at 540 g/m3. This variance in the lime usage is not clear, as there would have been no alkalinity remaining at pH below 4.5 pH units. It is assumed that there would have been other competing ions that would react with lime giving different lime usage requirements for different trial runs. 300542258:TJ506157NZPR Phosphorus Removal The objective of the trial was to determine the removal of phosphorus, especially dissolved 5 reactive phosphorus (DRP).

For all except two trials the overall DRP removal was above 95%. The exceptions showed overall DRP removal efficiencies of 89% and 87% respectively. If these two trial results are considered as outliers (providing much higher discharge DRP concentrations), then the discharge DRP concentrations in all other trials ranged between 0 0.06 - 0.98 g/m3 providing an average DRP removal of 97%.

A summary of the average percentage removals for all the phosphorus species is given in Table 3 for all the trials (excluding the "outlier" Trials). The total phosphorus (TP) and total dissolved phosphorus (TDP) data is based on 6 trials when these parameters were analysed.

Table 3: Phosphorus Removal Efficiencies In the Trials Parameter influent Cone.

Acid Phase Lime Phase Overall Discharge Cone.

TP 48. .1% 52.5% 77.6% 8.3 TDP 38. .8% 84.6% 95.4% 1.38 DRP . 9% 96% 97% 0.43 Notes: 1. 2 3 TP = Total phosphorus, TDP = Total dissolved phosphorus, DRP = Dissolved reactive phosphorus. Discharge concentration as an average actual sampled result measured in g/m3.

The discharge concentration has the dilution effect of the whitewater.

The alkaline phase effluent discharge concentration has not been corrected to account for the whitewater. This has been done purposely to show the actual discharge concentration rather than a mass discharge rate to demonstrate the achievable 20 performance standard in terms of the discharge concentration of DRP to be below 1 g/m3. However, the dilution effect of the whitewater is considered in the intermediate stages when determining percentage removal efficiencies between the acid phase, alkaline phase and overall phosphorus removal efficiencies.

The average DRP discharge concentration was found to be well below the target level of 25 1 g/m3 as identified in the objective. Whilst there is a contributory dilution effect with the 300542258:TJ506157NZPR 16 addition of whitewater, the effect of this only becomes important when determining mass loading and inter-stage (between acid and alkaline phase) removal efficiency calculations.

The lowest achievable DRP concentration after the alkaline phase discharge was 0.06 5 g/m3, well below the target concentration of 1 g/m3, however, this result was not repeatable in any other trials. The median DRP concentration was 0.45 g/m3.

Organic Load and Nutrient Removal There were 6 trials where a complete suite of common wastewater contaminants were ^jlO characterised (as shown in Table 2). This was undertaken to determine the variability of the raw effluent streams utilised for the various trials and to provide a performance assessment of the increase in contaminant removal with the addition of alkaline phase treatment.

Table 4 shows the percentage removal in various phases and the overall contaminant 15 removal based on the average concentrations of the trials in each phase. An average concentration of the final discharge is also provided.

Table 4: Other Contaminant Removal Efficiencies Parameter Acid Phase Alkali Phase Overall Discharge (g/m3) Biochemical oxygen demand 67% .6% 82.6% 302 Soluble biochemical oxygen demand 16.7% 32.4% 49.1% 157 Total chemical oxygen demand 74% 12.5% 86.5% 485 Soluble chemical oxygen demand 13.4% 28.4% 41.8% 424 Total Kjeldahl nitrogen 46.1% .2% 66.3% 50.5 Total ammoniacal nitrogen 41.6% 18.5% 60.1% 9.3 Notes: 1. The trials where full suite analysis was undertaken were Trials 3 and 9-13. 2. The discharge concentration is the actual average discharge after the alkaline phase. This result is not corrected t o take into effect of the whitewater added in both the acid and alkaline phase.

A large proportion of carbonaceous biochemical oxygen demand (BOD5) is removed in the acid phase, however, the results suggest that there is a substantial removal of soluble BOD5 in the alkaline phase. This is confirmed by the increase in the soluble COD removal rates in the alkaline phase. The nitrogen concentration in the alkaline phase 300542258:TJ506157NZPR 17 reduced by 20% in addition to the 46% removal achieved in the acid phase.

Overall, the addition of an alkaline phase for the removal of DRP also provided a moderate increase in the removal of other contaminants. Whilst not all soluble components could be removed from the raw effluent stream, there has been a reduction of up to 30% of 5 the compounds demanding degradation (oxygen demand).

Microbial Contaminant Removal For two trials an ultraviolet disinfection unit was added downstream of the alkaline phase discharge to determine the suitability of the discharged effluent for microbial disinfection.

^I0 The alkaline phase discharge wastewater was analysed for its transmittance and absorbance characteristics as well. The absorbance at 254 nm was 0.456 AU (1 cm cell) and the transmittance at 254 nm was 35.2% (1 cm cell). The microbial enumeration included faecal coliform, E.Coli, Cryptosporidium and Giardia.

The first trial was run at 3 pH units during the acid phase whereas the second was run 15 at 4 pH units for the acid phase. The alkaline phase was run at 9.5 pH units. The results of the enumeration for the acid phase run at 3 pH units is given in Table 5.

Table 5: Microbiological Results — Acid Phase 3 pH Units Parameter Influent Acid Phase Alkaline phase PostUV Faecal coliform .2E+06 1,300 320 7 E.Coli 4.23E+06 1,140 240 7 Cryptosporidium NE 1 Giardia NE 1 Notes: 1. The faecat coliform and E.Coli. results are based on average of 3 discrete samples during acid phase of pH 3 units. 2. Faecal Coliform and E. Coli are cfu/100 mL. 3 Cryptosporidium i s enumerated as presumptive at number per 100 L. 4. Giardia i s enumerated as presumptive at number per 100 L.

. NE = not enumerated. 300542258:T J506157NZPR 18 A summary of the microbial removal when the acid phase was at 4 pH units is given in Table 6.

Table 6: Microbiolo; jical Results — Acid Phase 4 pH Units Parameter Influent Acid Phase Alkaline phase Post UV Faecal coliform 6.9E+06 ,800 970 < 2 E.Coli 3.1E+06 8,200 713 < 2 Cryptosporidium NE < 1 Giardia NE < 1 Notes: 1. The faecal coliform and E.Coli. results are based on average of 3 discrete samples during acid phase of pH 3 units. 2. Faecal Coliform and E. Coli are cfu/100mL. 3- Cryptosporidium i s enumerated as presumptive at number per 100 L 4. Giardia i s enumerated as presumptive at number per 100 L.

. NE = not enumerated.

The data suggests that there is progressive reduction of faecal coliform and E. Coli. when treated in the pilot plant through the acid and alkaline phase. There is also an additional marginal reduction of faecal coliform and E.Coli when the pH was reduced in the acid phase to 3 pH units.

The Giardia and Cryptosporidium results showed similar responses.

Effect on pH Set-Point on Contaminant Removal As mentioned above, the set point of acid phase pH contributed to a marginal increase in removal of the microbial contaminants, especially, faecal coliform and E. Coli. However, an analysis of the nutrient removal dataset suggests that there has also been a marginal improvement in the removal rate of ammoniacal nitrogen and phosphorus species.

Float Sludge Characterisation The pilot scale DAF plant is designed to produce float sludge that is high in solids. Sludge was sampled from the two runs used to determine microbial contaminant removal. Sludge samples were taken for the acid phase (pH 3 and pH 4 on two separate runs), alkaline phase (pH = 9.5) and the mixed sludge from the two phases during each run.

The acid phase sludge from both runs showed a high level of solids. The alkaline phase 300542258:TJ506157NZPR 19 sludge tended to be low in solids and had a foamy texture. The highest sludge solids concentration achieved was 13% during acid phase.

The sludge from the acid phase, alkaline phase and the mixed samples was analysed for some metals and nutrients and are listed in Table 7 and 8. A preliminary examination of 5 the nutrient status of the sludge samples were undertaken, however, no further assessment of the sludge is undertaken in terms of mass balance for the pilot scale DAF system.

Table 7: Sludge Analysis for Acid Phase Run at 3 pH Units Parameter Acid Phase Alkaline phase Mixed sample Approximate sludge volume (L) 55 12 67 pH (pH units) .1 11.6 .6 Dry Matter solids (%) 13.0 3.07 9.8 Total recoverable calcium 1,440 ,780 ,300 Total recoverable magnesium 504 261 665 Total recoverable sodium 319 1,629 571 Total recoverable potassium 221 502 460 Ammonium nitrogen 500 345 1,650 Total nitrogen (g/100 g dry wt) 6.53 0.90 6.32 Nitrate nitrogen 13 29 9 Nitrite nitrogen 3 3 <1 Total recoverable phosphorus 4,220 6,320 7,220 Sulphate 9,170 3,750 ,340 Total recoverable boron < 20 0 < 20 Total recoverable chromium 4 1 4 Oil & grease 205,000 2,600 246,000 Notes: 1. All units in mg/kg dry weight unless stated otherwise. 2. The alkaline phase sample was greater than 96 % water and the analysis was undertaken as effluent water samples, however, the results above are correlated back to sludge equivalent samples. This has significantly skewed the sludge data as it is assumed that all the contaminants were bound in the sludge, which i s not the case. The results are reported as for sludge sample t o provide a simple comparison. 3. The nitrogen results, especially ammoniacal nitrogen for the mixed samples seemed t o be higher than the equivalent mass calculation for the acid phase and alkaline phase sludge, possibly as a result of mineralisation.

A similar sludge analysis profile was undertaken when the acid phase was run at pH 4.0. 10 The alkaline phase sludge did not have a large amount of solids and the estimated volume of sludge was about 20% of the acid phase, however, the solids content was 22 times less than that of the acid phase. 300542258:TJ506157NZPR Table 8: Sludge Analysis for Acid Phase Run at 4 pH Units Parameter Acid Phase Alkaline phase Mixed sample 84 Approximate sludge volume (L) 70 14 pH (pH units) .3 8.8 6.6 Dry Matter solids (%) .1 0.45 9.4 Total recoverable calcium 2,030 451,600 2,530 Total recoverable magnesium 490 ,390 516 Total recoverable sodium 648 13,480 646 Total recoverable potassium 410 ,170 417 Ammonium nitrogen 1,590 2,630 2,850 Total nitrogen (g/100 g dry wt) .44 4.51 .45 Nitrate nitrogen 1 165 1 Nitrite nitrogen 2 3 Total recoverable phosphorus 3,590 97,750 3,990 Sulphate 3,480 31,685 3,790 Total recoverable boron < 20 0 <20 Total recoverable chromium 4 0 3 Oil & grease 430,000 44,940 552,000 Notes: 1. AH units in mg/kg dry weight unless stated otherwise. 2. The alkaline phase sample was greater than 9 9% water and the analysis was undertaken as effluent wat samples, however, the results above are correlated back t o sludge equivalent samples. This has signifkan skewed the sludge data as it i s assumed that all the contaminants were bound in the sludge, which / s / the case. The results are reported as for sludge sample t o provide a simple comparison.

The sludge contains high levels of nutrients, which provides an excellent soil 5 conditioning for land disposal, however, the level of oil and grease was also high and may provide some constraints for higher land application rates.

The amount of nitrogen, especially ammoniacal nitrogen seemed to have increased in the mixed sample. This could have resulted from mineralisation of total Kjeldahl nitrogen when the low pH sludge was mixed with the high pH sludge. Further characterisation is 10 required to determine the mixing effect on the sludge nitrogen transformation.

Whilst detailed analysis of the actual sludge mass loads have not been calculated in these 2 trials (the volumes were provided as approximate), some general trends have been apparent. Apart from higher phosphorus recovery in alkaline (lime) phase, there seems to be an increased removal of ammonia nitrogen, sulphate, sodium, potassium and 15 magnesium. Whilst some of this may be contributed from mineralisation and the impurities 300542258:TJ506157NZPR 21 in the hydrated lime added in the alkaline phase, it is likely that some of the contaminants from the liquid phase may have precipitated out in the sludge. Further work is required to verify this.

Pilot Plant Trial Outcomes The results from the trial have confirmed that nearly all DRP can be removed from the raw effluent streams via DAF in series treatment, using hydrated lime as a reactant for the phosphorus removal phase.

In addition to the removal of more than 95% of DRP, total phosphorus (TP) and total ^^0 dissolved phosphorus (TDP) can be removed in significant amounts. The trials suggested that more than 77% of TP is removed while TDP removal exceeded 95%.

There was a marginal increase in the removal rate of phosphorus when the acid phase of the DAF was run at 3 pH units. However, there is a distinct increase in the removal rate of the microbial contaminants, especially faecal coliform and E. Coli. when a lower acid 15 phase pH set point is utilised in conjunction with a alkaline phase test.

Other contaminant removal was also significant. Whilst a large proportion of the contaminant removal was achieved in the acid phase as a result of the removal of solids, there is a slight increase in the removal of contaminants especially for soluble biochemical oxygen demand (SBOD) and soluble chemical oxygen demand (SCOD) as 20 shown in Table 4 and Figure 2.

The disinfection trials show that that is an improvement of microbial water quality with the addition of the alkaline phase using hydrated lime and a substantial die off in the ultraviolet disinfection unit.

Overall, use of acid and alkali DAF units in series provided an unexpectedly good 25 pollutant removal efficiency, in particular in relation to dissolved reactive phosphorus (DRP) and microbial contaminants. The process offers benefits to industries that create wastewater including protein, DRP etc. and allows effective post DAF treatment to remove microbials as well.

The foregoing describes the invention including preferred forms thereof. Alterations and modifications as would be known to a skilled person are intended to be included within the scope and spirit of the invention and defined in the attached claims. 300539934:TJ506157NZPR 22

Claims (5)

CLAIMS:

1. A method of wastewater treatment including the following steps: 5 (a) treating the wastewater in a first acid phase DAF unit at a pH above the level that results in substantial splitting of haemoglobin, together with a suitable polymer flocculating agent; (b) removing the flocculated components; (c) treating the wastewater from step (b) in a second alkaline phase DAF unit at a 10 pH above about pH 9.0, together with a suitable polymer flocculating agent; and (d) removing the flocculated components.

2. The method of claim 1 wherein the wastewater from step (b) is collected prior to 15 the alkaline phase.

3. The method of any one of the preceding claims wherein the pH of the acid phase is held above pH 3.0. 20

4. The method of any one of the preceding claims wherein the pH of the acid phase is held below about 4.5.

5. The method of any one of the preceding claims wherein the pH of the alkaline phase is held above about 9.0. 25

6. The method of any one of the preceding claims wherein the pH of the alkaline phase is held below about 11.5.

7. The method of any one of the preceding claims wherein the acid in the acid phase 30 is sulfuric acid.

8. The method of any one of the preceding claims wherein the alkali in the alkaline phase is hydrated lime. 35 9- The method of any one of the preceding claims wherein the polymer flocculating agent is a cationic and/or anionic polymer. 300711342:T J506157N2PR 10. 5 11. 12. 10 13. 14. 15 15. 20 25 16. 30 17. 18. 35 19. 23 The method of any one of the preceding claims further including the use of bentonite as an additional flocculating agent. The method of any one of the previous claims wherein the level of dissolved reactive phosphorus following wastewater treatment is below 1 g/m3. The method of any one of the previous claims further including the use of a microbial treatment step after the alkaline DAF phase. The method of any one of the previous claims further including filtering the wastewater before entry to the acid phase DAF unit. The method of any one of the preceding claims wherein the acid phase removes solids and ions that compete with phosphorus ion removal in the alkaline phase. A method of wastewater treatment including the steps of: (a) treating the wastewater in a first acid phase DAF unit, together with an inverse emulsion polymer flocculating agent, wherein the pH is between 3.0 and 4.5; (b) removing the flocculated components; (c) treating the wastewater from step (b) in a second alkaline DAF unit at a pH between about 9.0 and about 11.5 together with a cationic polymer flocculating agent; and (d) removing the flocculated component. The method according to claim 15 or 16 wherein the acid in the acid phase is sulfuric acid and the alkali in the alkaline phase is hydrated lime. The method according to claim 15 or 16 the acid phase pH is kept between 3.5 and 4.5. The method according to claim 17 wherein the alkaline phase is kept between 9.5 and 11.5. The method according to any one of claims 15 to 18 wherein t ' QFPIOF OF N.7- j^OPERTY 13 APR 2007 received. 300711342:T J506157NZPR 24 screened before entering the acid phase DAF unit.

20. The method according to any one of claims 15 to 19 wherein the wastewater is disinfected after step (d).

21. A wastewater treatment method substantially as herein described with particular reference to any one of the Examples, excluding prior art. 10 PATTLE DELAMORE PARTNERS LIMITED By Their Attorneys OFFIOF OF N./- I 1 3 APR 2007 , RECEIVES