WO2022146373A1

WO2022146373A1 - Ultrasound assisted thermophilic aerobic membrane distillation bioreactor (sono-mdbr) system and method developed for the treatment of hospital wastewater

Info

Publication number: WO2022146373A1
Application number: PCT/TR2021/051526
Authority: WO
Inventors: Mahir INCE; Elif INCE; Yasin Abdullah USLU; Handenur YASAR UYSAL
Original assignee: Gebze Teknik Universitesi
Priority date: 2020-12-29
Filing date: 2021-12-27
Publication date: 2022-07-07
Also published as: EP4271654A1; EP4271654A4; TR202022273A2

Abstract

The invention relates to an ultrasound (US) assisted thermophilic aerobic membrane distillation bioreactor (sono-MDBR) system and method developed for the treatment of hospital wastewater.

Description

ULTRASOUND ASSISTED THERMOPHILIC AEROBIC MEMBRANE DISTILLATION BIOREACTOR (SONO-MDBR) SYSTEM AND METHOD DEVELOPED FOR THE TREATMENT OF HOSPITAL WASTEWATER

Technical Field

Prior Art

Water recovery is very important in terms of both clean water scarcity and environmental pollution. Salts, nutrients (such as nitrogen, phosphorus), pathogens and micropollutants (MP) must be removed from the wastewater for a reliable water recycling. Among these pollutants, micropollutants are the main source of the problem, as conventional wastewater treatment plants are not specifically designed to treat these pollutants. Micropollutants may be present in wastewaters at concentrations of pg/L or lower. If they are not adequately removed, most micropollutants can cause negative effects on human health and the ecosystem, such as the formation of resistant bacteria. Therefore, these pollutants threaten the receiving environment where they are discharged as well as the reuse of wastewater.

The increase in micropollutant (MP) concentration in surface waters and groundwater has become increasingly noteworthy in recent years. Micropollutants consist of pollutants such as surfactants, pharmaceuticals and personal care products, endocrine disruptors, unregistered drugs, gasoline additives, etc. The consumption of pharmaceuticals in these pollutants is increasing year by year. Only a certain part of these drugs is metabolized after use. The nonmetabolized part is usually excreted from the body through the urine. Hospital wastewater, one of the most important sources of these pollutants, includes recalcitrant and toxic micropollutants resulting from metabolite products of drugs, chemicals, heavy metals, disinfectants and sterilizers, specific detergents of endoscopic and other devices, radioactive tracers and iodinated contrast media (ICM). A wide range of pharmaceuticals are used in hospitals for analysis, treatment, research and surgery. The change in the quantity and characterization of the pharmaceuticals used on an annual basis varies depending on the new laws, the use of new active substances and the decommissioning of some active substances.

Pharmaceuticals, complex compounds, whose molecular weights, structures, and functions are very different, are polar molecules with lipophilic properties. They contain multiple ionizable groups and their ionization degrees vary depending on the pH of the medium. These compounds can accumulate in some tissues, be absorbed, disrupt metabolic reactions and change the chemical structure. Disinfectants are used for disinfection of floors, device and skin disinfection and food preparation in hospitals. Chlorines containing recalcitrant such as alcohol, aldehyde and even chlorophenol are used as disinfectants. One of the important problems arising from hospital wastewater is that they contain microbial pollutants such as bacteria, viruses, and helminths. Microbiologic ally, hospitals have a lower load than domestic wastewater, but the real danger is the presence of antibiotic-resistant bacteria (Proteusvulgaris, Mycobacteria) and hospital-specific species (Enterobacter sakazakii, etc.). This resistance to antimicrobial agents causes more difficult diseases to occur.

Hospital wastewater usually enters classical domestic wastewater treatment plants together with domestic wastewater and then discharges into the receiving environment. However, many pollutants in hospital wastewater are highly resistant to biological degradation. The removal efficiencies of these pollutants in the domestic wastewater treatment plant have been investigated by many researchers. It is seen that the treatment efficiency varies between 10% and 90% when the literature on the treatment of pharmaceutical compounds is examined.

There are many studies on micropollutant removal with advanced oxidation processes such as fenton, UV, ozone. These processes are generally applied to the biological treatment outlet in hospital wastewater treatment, but when applied on their own, the full mineralization efficiency is fairly low. Intermediate products formed in partial degradation may be more toxic than the parent compound or have the same properties as the parent compound. Integrated advanced oxidation processes such as Ch/Fenton, O3/H2O2, O3/UV, Ch/Photo- Fenton can be used for the complete mineralization of micropollutants, but high operating and initial investment costs arise due to these methods.

Membrane bioreactors (MBR), which are very advantageous against classical activated sludge systems, are an alternative wastewater treatment system. MB Rs are formed as a result of the combination of MF (microfiltration) and UF (ultrafiltration) membranes, which are low pressure membranes, with the active sludge system. MBRs are generally operated at high biomass concentrations (10-20 g/L) and high sludge ages (10-30 days), and consequently produce better quality effluent and less waste sludge compared to the conventional activated sludge system. In addition, MBRs for the same treatment capacity require less space and volume than the conventional active sludge system.

Extensive studies have been carried out in recent years on the micropollutant removal performances of MBRs. Since hydrophobic micropollutants can remain in the bioreactor for longer in MBRs with high sludge age as adsorbed on biomass, it has been found that their removal is high, while some hydrophilic micropollutants such as carbamazepine and diclofenac have similar removal efficiency in MBRs to that in the conventional active sludge system. The duration of stay of hydrophilic and biodegradation-resistant micropollutants in MBRs is the same as the hydraulic residence time (HRT) since micropollutants can pass freely through MF and UF membranes. The hydraulic residence time (HRT) may be shorter especially in MBRs operated at high MLSS (Mixed Liquor Suspended Solids) concentrations. Therefore, advanced treatment methods such as reverse osmosis (TO), nanofiltration (NF), UV oxidation or ozonation are generally recommended for the removal of micropollutants in MBR effluent. Even though quality water can be obtained with these multiple treatment systems, it overshadows the advantage to be obtained by re-using wastewater due to the high investment and operating costs and the need for more construction areas.

The continuous development of MBRs has led to the emergence of the new high retention capacity MBR (HR-MBR) concept. HR-MBRs combine biological wastewater treatment system and membrane module with high retention capacity in a single system. The pollutants in question can stay in the bioreactor for a longer time and their biodegradation is possible since the membranes with high retention capacity keep the MPs in the system. Since HR- MBRs can efficiently treat micropollutants, they make it possible to treat wastewater up to drinking water quality with only a single treatment step or discharge the effluent into sensitive areas. There are three different HR-MBRs studied in the literature. These are NF-MBR (MBR using NF membrane instead of MF/UF membrane), OMBR (MBR using advanced osmosis membrane instead of MF/UF membrane) and MDBR (MBR using distillation membrane instead of MF membrane). In the studies conducted with NF-MBR and OMBR, both the very low flux obtained and the high energy requirement due to the pressure applied make MDBR more advantageous for industries with waste heat and the possibility of using solar heat. There are species of microorganisms that can live in deadly temperatures for most life forms. The metabolic rates of these microorganisms living at high temperatures (thermophilic microorganisms) are fairly high. Therefore, they can be used for the rapid treatment of organic wastes. Thermophilic wastewater treatment is the treatment of wastewater consisting of different sources by increasing the temperature above 45°C and to a maximum of 70°C. Thermophilic aerobic wastewater treatment has some advantages compared to conventional systems such as more degeneration rate, inactivation of pathogens, low sludge production and process stability. Thus, the main cost will decrease as the retention time required for treatment will be reduced. Meanwhile, thermophilic treatment is stable in case of deterioration of conditions. Another advantage of thermophilic bacteria is that they destroy the microorganisms causing the disease at temperatures of 55°C and above. Some pollutants, which are slow biodegradable, can also be broken down more rapidly with thermophilic treatment. The rate of degeneration of micropollutants, which are examples of these pollutants, increases with thermophilic treatment.

Thermophilic systems, in particular, can be applied for wastewaters with high pollution load and low flow rate, wastewaters with high salinity or containing hazardous compounds. Thermophilic treatment of high strength and/or high temperature wastewaters such as domestic paper, chicken slaughterhouse, beer, synthetic, fruit industry has been investigated, and studies have shown that it is effective even in the treatment of high strength landfill wastewaters. This technology has started to be widely used for the treatment of various types of wastewater in recent years. The permeate quality in MDBR is of TO permeate quality and is independent of biological activity. Since the continuity of the permeate quality can be ensured even in case of low bioactivity in the reactor, it is resistant to shock loading and operating problems. The permeate quality obtained in a single system with MDBR is the same as the conventional activated sludge system + MF + TO or the effluent quality obtained by multiple systems such as MBR + TO. The time required for commissioning is much shorter than the classical MBR since the quality of the permeate in MDBR is not dependent on the bioactivity in the reactor. The pollutants, which are slow biodegradable and recalcitrant, stay in the bioreactor for a longer period of time, thereby it is possible to break them down. Since MDBR is a system operated under atmospheric conditions, its dependence on electrical energy is less than pressure systems. The need for thermal heat can be provided from waste heat or solar energy.

Non-volatile compounds are completely retained, while volatile compounds can pass through the membrane in the membrane distillation (MD) process. However, biological degradation can contribute to the removal of volatile compounds in wastewater. This shows that MDBR has the potential to completely treat almost all organic pollutants. The main differences between MDBR and conventional MF/UF-MBRs are summarized in Table 1. An important point to note is that non-volatile compounds such as salt are kept in the process and accumulated until they are disposed of with waste sludge.

Table 1: Differences between MF/UF-MBR and MDBR

The comparison of MDBR with MBR + TO in terms of cost is given in Table 2. Both investment and maintenance costs of MDBR are cheaper than MBR + TO system as can be seen from Table 2. The most important reason for this is that MDBR can be operated in a single system and under atmospheric conditions.

Table 2: Economic comparison of MF/UF-MBR + TO and MDBR systems

The use of ultrasound (US) causes periodic compression and thinning (thinning) in the liquid.

Meanwhile, the bubbles formed grow and deflate in a few microseconds. This process is called “cavitation”. Earge cavitation bubbles occur at low frequencies and exert a very strong hydromechanical shear force. The pressure and temperature in the cavitation bubble rise rapidly throughout the adiabatic bubble deflation. Therefore, each bubble in the liquid can be thought of as a microreactor. The sonochemical process resulting from the high temperature and pressure in the bubble includes pyrolytic reactions and hydromechanical effects due to cavitation in addition to the OH- radical, unlike other advanced oxidation processes. US has been used for the degradation of many different pollutants such as chlorinated solvents, hydrocarbons, pesticides, phenols and polymers. It is reported in the literature that pollutants cause high energy consumption as they require complete mineralization with US for quite a long time. Therefore, it is more suitable to be used in combination with other treatment processes.

The combination of US and biological treatment is a promising new technique in the field of wastewater treatment. Factors limiting biodegradation can be eliminated by sonication. In addition, the removal of the remaining pollutants in the environment by biodegradation is more economical than the complete removal by US, as a result of US application.

Two types of strategies are followed for the combination of US and biological treatment. These are the simultaneous application of US and biological treatment and the application of biological treatment after ultrasonic pre -treatment. The growth rate of the microorganisms should be more or at least equal to the inactivation of the microorganism caused by US in the method where US and biological treatment are applied at the same time. Therefore, knowing the US parameters that cause the inactivation of microorganisms is a prerequisite in the design of US assisted bioreactors. Studies in the literature indicate that there is a possibility that low- frequency US will not harm microorganisms only when applied for a short time and at a very low severity. It is possible that active microorganisms are exposed to US for a longer period of time by reducing the severity.

The structure and properties of some microorganisms affect their sensitivity to US. It has been reported in studies conducted with pure cultures that cell size, shape, composition of the cell wall and physiological status of microorganisms affect their sensitivity to US.

In addition, US increases fluid mixture and mass transport. Thus, it is known that enzymes accelerate the transport of nutrients to their active points and the removal of microbial waste products from these active points. Short-term application periods damage the cell at a level that it can tolerate and increase the membrane permeability of the cell. However, if US is applied continuously, cell destruction increases and bioactivity decreases. The increase in bioactivity with short-term application periods is due to the activation of defense mechanisms because microorganisms are exposed to US. Therefore, since different microorganisms will have different defense mechanisms, they will react differently to the US application of the same frequency and power.

(When US is applied directly to microbial culture at low power densities;

(i) Mass transfer inside and outside the cell increases due to increased cell membrane permeability.

(ii) When microorganisms are exposed to US, they increase their bioactivity by activating defense mechanisms under stress.

(iii) It increases the biodegradation efficiency of pollutants with the increase in mass transfer with microjets formed due to low hydromechanical effect.

The China patent document CN103304109A, which is the state of the art, mentions the treatment of hospital wastewater by using biological treatment and membrane. The submerged UF membrane was preferred to make a solid liquid separation and no application was included to increase bioactivity in this patent.

A study is mentioned in the Japan patent document JP5097024B2, which is the state of the art, which aims to create bubbles of different sizes and to treat with nanobubbles in particular. US was also used to produce the nanobubble, which is the main purpose of the study. However, there is no purpose that increases bioactivity in any biological treatment even though the objective of the study is not the treatment of hospital wastewater.

A process containing MD, which aims to obtain fresh water from salt waters, is mentioned in the United States patent document US4460473A, which is the known state of the art. Salt and surfactants in sea water are removed with the process. There is a need to develop a US assisted thermophilic aerobic membrane distillation bioreactor (Sono-MDBR) system and method for the treatment of hospital wastewater when the systems and methods available in the art are examined.

Objects of the Invention

The object of the present invention is to realize the Sono-MDBR system and method developed for the treatment of hospital wastewater.

Another object of this invention is to realize the Sono-MDBR system and method, which performs well for industries producing recalcitrant and toxic wastewater, such as hospital wastewater, and where the effluent can be used directly (without additional treatment).

Detailed Description of the Invention

The Sono-MDBR system for achieving the objects of the present invention is shown in the accompanying figures.

These figures are as follows;

Figure 1: A schematic view of the US assisted thermophilic aerobic membrane distillation bioreactor (MDBR) system of the invention.

The components in the figures are individually numbered and their corresponding numbers are given below.

1. Reactor

2. MD module

3. Transducer

4. US generator

5. Diffuser

6. Air compressor 7. Balancing tank

8. Permeate collection tank

9. Peristaltic pump

10. Probe

11. Heater

12. Cooler

13. PLC

The present invention relates to the Sono-MDBR system developed for the treatment of hospital wastewater and comprises the following elements:

- A reactor (1) with thermophilic aerobic bioculture and covered with a heat jacket,

- MD module (2), which is immersed in the reactor (1) and used to obtain distillate,

- Transducer (3), which is flanged to the base of the reactor (1) and enables the US to be transmitted to the reactor (1),

- US generator (4) connected with the transducer (3) and generating the US that the transducer applies to the active sludge in the reactor (1),

- Diffuser (5), which is located in the reactor (1) and provides the the oxygen demand of the aerobic culture and the control of the contamination that will occur on the membrane surface,

- Air compressor (6) connected to the diffuser (5) and providing the air requirement of the system,

- Balancing tank (7) connected with the reactor (1) and containing the wastewater to be given to the system,

- Permeate collection tank (8) containing distillate passing through the membrane and water circulated to the MD module (2)

- Peristaltic pump (9) providing wastewater supply to the system positioned between the balancing tank (7) and the permeate tank (8) and the reactor (1) and water circulation in the MD module (2),

- Probes (10) in contact with thermophilic aerobic bioculture and permeate water in the reactor (1), - Heater (11) connected with the reactor (1) and providing the heating of the reactor (1) to the temperature required for the thermophilic conditions and MD,

- Cooler (12), which is positioned between the permeate collection tank (8) and the reactor (1) and in which the water circulated in the MD module (2) is cooled,

- PLC (13) connected with the probes (10) and where the control, recording and monitoring of the system parameters such as water level, pH, conductivity, flux of the reactor (1) taken with the probes (10).

The present invention relates to the Sono-MDBR method developed for the treatment of hospital wastewater and comprises the following steps;

- Giving hospital wastewater via peristaltic pump (7) to the reactor (1) where thermophilic aerobic mixed culture is located,

- Applying ultrasound to the thermophilic mixed microorganism culture in the reactor (1) in order to increase bioactivity,

- Measuring the temperature, conductivity, pH, dissolved oxygen concentration values of the US applied thermophilic active sludge as well as the conductivity and temperature values of the permeate with probes (10),

- Circulating the permeate flow via the peristaltic pump (7) from the submerged direct contact MD module (2) to the permeate tank (8) and then to the cooler (12),

- Finally, removing the excess of treated hospital wastewater from the permeate collection tank (8).

US generator (4) with 20 kHz frequency is used in which hospital wastewater is treated with Sono-MDBR system in the system of the invention. Ultrasound (US) is applied to the thermophilic mixed microorganism culture in MDBR at a power density of 5.4 W/L for 12.5 minutes in 24 hour periods in order to increase bioactivity in the system. In addition, a "silent" (non-US) control operating under the same operating conditions as sono-MDBR was operated for MDBR comparison.

The US is applied to thermophilic aerobic bioculture with the transducer (3), which is flanged to the base of the reactor (1) in the system of the invention. The reactor (1) is made of stainless steel material so that its connection with the transducer (3) is smooth and the cavitation does not damage the walls. The system consists of the main bioreactor (1), the submerged direct contact distillation membrane module (2), the balancing tank (7), the permeate collection tank (7), the PLC control unit (13) and the ventilation system. MD module (2) in MDBR was placed in the bioreactor (1), leaving it outside the cavitation area and paying attention to the sufficient air stripping. Air is supplied to the system with an air compressor (6) for both oxygen demand and suspension of the aerobic culture in the reactor (1) and for controlling the pollution that will occur on the surface of the submerged distillation membrane.

The temperature, conductivity, pH, dissolved oxygen concentration of the thermophilic active sludge, and the conductivity and temperature of the permeate are measured with probes (10) and continuously monitored with PLC (13). The permeate flow is circulated via the peristaltic pump (9) from the submerged direct contact MD module (2) to the permeate collection tank (8) and then to the cooler (12). The reactor (1) was surrounded by a heat jacket and kept at a constant temperature with the help of a heater (11) in order to keep the operating temperature (55.5±1°C) under control. The temperature of the permeate circulated on the other side of the membrane is kept constant at 19.5±1°C. There is a hydrophobic PVDF (Polyvinylidene Fluoride) membrane with a nominal pore diameter of 0.2 pm, a porosity of 0.75 and a thickness of 200 pm in the direct contact MD module (2) in the MDBRs. The MD module (2) is directly immersed in the thermophilic active sludge. Thus, thermophilic active sludge is in direct contact with the membrane surface. The distillation membrane was placed far enough away that it would not be affected by the ultrasound applied in thermophilic active sludge cavitation and microbes. Otherwise, there is a possibility of wetting and/or damage to the membrane. Raw hospital wastewater is fed to the reactor (1) automatically by the PLC (13) with level control and with the help of the peristaltic pump (9).

The system and method of the invention is a study in which ultrasound is applied to MDBR and ultrasound is applied to classical aerobic thermophilic active sludge whose bioactivity (growth rate, endogenous respiration, enzymatic activity, etc.) is different from mesophilic aerobic active sludge. Both hospital wastewater and micropollutants are treated with ultrasound (US) assisted thermophilic MDBR thanks to the system and method of the invention.

In the system and method of the present invention, the treatment of hospital wastewater was 5 carried out with the sono-MDBR system having important wastewater treatment advantages as mentioned above, which is made as a compact reactor by combining MD, thermophilic biological treatment and ultrasound. In COD (Chemical oxygen demand), BOD (Biochemical oxygen demand), AOX (Absorbable organic halogens), chloride and orthophosphate a removal efficiency over 99.9% was obtained, while in sono-MDBR and control-MDBR a 0 TOC (Total organic carbon) removal efficiency of 99.63% and 99.59% were achieved, respectively when the pollutant concentrations in the effluent are examined.

The removal efficiencies of the micropollutants detected in the hospital wastewater in the sono-MDBR where ultrasound (US) is applied and non-US control-MDBR, and the 5 comparison of these pollutants with the removal efficiencies obtained in other studies in the literature are shown in Table 3. The majority of micropollutants have been almost completely removed according to the data in Table 3.

Table 3: Comparison of MDBR removal efficiencies of micropollutants detected in hospital wastewater with some studies in the literature and % removal efficiencies

Claims

1. A Sono-MDBR system developed for the treatment of hospital wastewater characterized in that it comprises the following elements:

- Membrane distillation module (2) immersed in reactor (1),

- Ultrasound generator (4) connected with the transducer (3) and generating the US that the transducer applies to the active sludge in the reactor (1),

- Probes (10) in contact with thermophilic aerobic bioculture and permeate water in the reactor (1),

2. The Sono-MDBR system developed for the treatment of hospital wastewater according to claim 2 characterized in that it comprises a diffuser (5), which is located in the reactor (1) and provides the oxygen demand of the aerobic culture and the control of the contamination that will occur on the membrane surface.

3. The Sono-MDBR system developed for the treatment of hospital wastewater according to claim 2 characterized in that it comprises an air compressor (6) connected to the diffuser (5) and providing the air requirement of the system.

4. The Sono-MDBR system developed for the treatment of hospital wastewater according to any one of the preceding claims, characterized in that it comprises a balancing tank (7) connected with the reactor (1) and containing the wastewater to be given to the system.

5. The Sono-MDBR system developed for the treatment of hospital wastewater according to any one of the preceding claims, characterized in that it comprises a permeate collection tank (8) containing distillate passing through the membrane and water circulated to the MD module (2).

6. The Sono-MDBR system developed for the treatment of hospital wastewater according to any one of the preceding claims, characterized in that it comprises a peristaltic pump (9) providing wastewater supply to the system positioned between the balancing tank (7) and the permeate tank (8) and the reactor (1) and water circulation in the MD module (2).

7. The Sono-MDBR system developed for the treatment of hospital wastewater according to any one of the preceding claims, characterized in that it comprises a heater (11) connected to the reactor (1) and providing the heating of the reactor (1) to the temperature required for the thermophilic conditions and MD.

8. The Sono-MDBR system developed for the treatment of hospital wastewater according to any one of the preceding claims, characterized in that it comprises a cooler (12) positioned between the permeate collection tank (8) and the reactor (1) and in which the water circulated in the MD module (2) is cooled.

9. The Sono-MDBR method developed for the treatment of hospital wastewater, characterized in that it comprises the following steps:

- Applying US to the thermophilic mixed microorganism culture in the reactor (1) in order to increase bioactivity,

- Measuring the temperature, conductivity, pH, dissolved oxygen concentration values of the US applied thermophilic active sludge as well as the conductivity and temperature values of the permeate with probes (10), - Circulating the permeate flow via the peristaltic pump (7) from the submerged direct contact MD module (2) to the permeate tank (8) and then to the cooler (12),

10. The Sono-MDBR method developed for the treatment of hospital wastewater according to claim 9, characterized in that US is applied to the thermophilic mixed microorganism culture in the reactor (1) at a power density of 5.4 W/L for 12.5 minutes in 24 hour periods in order to increase bioactivity.

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