Reducing herbicide discharge to sensitive environments using membrane bioreactors

A hybrid MBR/UV/GAC treatment system was researched to remove Ametryn, which is a commonly used herbicide in Australian farmlands, from wastewater. The research revealed that the hybrid system could be successfully used for 100% removal of Ametryn. Two mathematical models were developed to predict the frequency of chemical cleaning of MBR-membrane and the mechanism of fouling of membrane.

Implications of short and long term critical flux experiments for laboratory-scale MBR operations

This paper evaluates the critical flux obtained by different techniques including tests with different flux step lengths (20 and 40 min and 7 days) and modes of operation (continuous and intermittent) under low and high MLSS concentrations. The paper also analyses a couple of long-term tests (flow rate of 40 and 20 L/day) to obtain the time required to reach the critical flux experimentally and compares those values with the results obtained numerically from a mathematical model. It was found that intermittent mode with membrane relaxation was useful in controlling the fouling of membrane and in restoring the membrane from fouling at lower MLSS.

Comparative study on performance of yeast and bacterial membrane bioreactors for high salinity wastewater treatment

Two laboratory-scale membrane bioreactor systems were investigated to treat high saline wastewater containing 1,000 mg/L COD and 32 g/L NaCl, namely: the yeast membrane bioreactor (YMBR) and the bacterial membrane bioreactor (BMBR). COD removal of both processes was above 90% at a hydraulic retention time (HRT) of 5 hours (volumetric loading of 5 kg COD/m³.d), sludge retention time (SRT) of 50 days (the MLSS of above 14 g/L and the F/M of 0.4 d-1). Under these operating conditions, the YMBR could run at a ten-fold lower transmembrane pressure with significantly reduced membrane fouling rate compared to BMBR. This may be because of low production of adhesive extracellular polymers (ECP) and the secondary filtration layer formed from large yeast cells. ECP production of bacterial sludge was increased considerably at high salt concentrations (32 g/L and 45 g/L) and long SRTs. For the bacterial sludge, the increased salinity led to increase in ECP, whereas the ECP content of the yeast sludge was relatively small.

Removal of ametryn using membrane bioreactor process and its influence on critical flux

Compared to the Conventional Activated Sludge Process (ASP), Membrane Bioreactors (MBRs) have proven their superior performance in wastewater treatment and reuse during the past two decades. Further, MBRs have wide array of applications such as the removal of nutrients, toxic and persistent organic pollutants (POPs), which are impossible or difficult to remove using ASP. However, fouling of membrane is one of the main drawbacks to the widespread application of MBR technology and Extra-cellular Polymeric Substances (EPS) secreted by microbes are considered as one of the major foulants, which will reduce the flux (L/m2/h) through the membrane. Critical flux is defined as the flux above which membrane cake or gel layer formation due to deposition of EPS and other colloids on the membrane surface occurs. Thus, one of the operating strategies to control the fouling of MBRs is to operate those systems below the critical flux (at Sub-Critical flux). This paper discusses the critical flux results, which were obtained from short-term common flux step method, for a lab-scale MBR system treating Ametryn. This study compares the critical flux values that were obtained by operating the MBR system (consisting of a submerged Hollow-Fibre membrane with pore size of 0.4μm and effective area of 0.2m2) at different operating conditions and mixed liquor properties. This study revealed that the critical flux values found after the introduction of Ametryn were significantly lower than those of obtained before adding Ametryn to the synthetic wastewater. It was also revealed that the production of carbohydrates (in SMP) is greater than proteins, subsequent to the introduction of Ametryn and this may have influenced the membrane to foul more. It was also observed that a significant removal (40-60%) of Ametryn from this MBR during the critical flux determination experiments with 40 minutes flux-step duration.

Performance of suspended and attached growth MBR systems in treating high strength synthetic wastewater

The performance of laboratory-scale attached growth (AG) and suspended growth (SG) membrane bioreactors (MBRs) was evaluated in treating synthetic wastewater simulating high strength domestic wastewater. This study investigated the influence of sponge suspended carriers in AG-MBR system, occupying 15% reactor volume, on the removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), and compared it to that of SG-MBR. Results showed that the removal efficiencies of COD, TN and TP in AG-MBR were 98%, 89% and 58%, respectively as compared to 98%, 74% and 38%, respectively in SG-MBR. Improved TN removal in AG-MBR systems was primarily based on simultaneous nitrification and denitrification (SND) process. These results infer that the presence of small bio-particles having higher microbial activity and the growth of complex biomass captured within the suspended sponge carriers resulted in improved TN and TP removal in AG-MBR.

Treatment of textile wastewater with membrane bioreactor: a critical review

Membrane bioreactor (MBR) technology has been used widely for various industrial wastewater treatments due to its distinct advantages over conventional bioreactors. Treatment of textile wastewater using MBR has been investigated as a simple, reliable and cost-effective process with a significant removal of contaminants. However, a major drawback in the operation of MBR is membrane fouling, which leads to the decline in permeate flux and therefore requires membrane cleaning. This eventually decreases the lifespan of the membrane. In this paper, the application of aerobic and anaerobic MBR for textile wastewater treatment as well as fouling and control of fouling in MBR processes have been reviewed. It has been found that long sludge retention time increases the degradation of pollutants by allowing slow growing microorganisms to establish but also contributes to membrane fouling. Further research aspects of MBR for textile wastewater treatment are also considered for sustainable operations of the process.

Biodegradation of pentachlorophenol in a membrane bioreactor

Pentachlorophenol (PCP) is a toxic chemical, often used in the formulation of pesticide, herbicide, anti fungal agent, bactericide and wood preservative. This study is aimed at evaluating the potential of membrane bioreactor (MBR) to treat PCP contaminated wastewater. Synthetic wastewater with COD of 600 mg/L was fed into the MBR at varied PCP loading rate of 12–40 mg/m3/d. A PCP removal rate of 99% and a COD removal rate of 95% were achieved at a hydraulic retention time of 12 hs and a mixed liquor suspended solids (MLSS) concentration of 10,000 mg/L. When sodium pentachlorophenol (NaPCP), which has higher solubility in water, was used in the second phase of the study, at loading rates varying from 20 to 200 mg/m3·d, the removal rate of NaPCP was higher than 99% and the removal rate of COD was more than 96%. It was also found that at higher biomass concentrations, biosorption played an important role besides the biodegradation process. Batch experiments conducted in this study revealed that the sorption capacity to be 0.63 (mg PCP/g biomass) and occurred rapidly within 60 min. This phenomenon could enhance the PCP degradation through increased contact between microorganism and PCP. Further, the membrane resistance was low (trans-membrane pressure of 14 kPa) even after more than 100 ds of operation. In addition, the toxic level of PCP in the influent could have induced the microorganisms to secrete more extra-cellular polymeric substances (EPS) for their protection, which in turn must have increased the viscosity of the mixed liquor.

Landfill leachate treatment using thermophilic membrane bioreactor

This study was undertaken to investigate the performance of aerobic thermophilic membrane bioreactor (MBR) treating raw landfill leachate from two landfill sites in Thailand (Pathumthani site and Ram Indra site). The leachates from these sites were mixed in different proportions to produce a BOD/COD ratio of 0.39, 0.57, and 0.65, which was investigated in 3 experimental runs. The COD, ammonia, and TKN composition of the mixed leachate was 12,000, 1700 and 1900 mg/L, respectively. BOD was supplemented with glucose and soy protein. The system was operated at 45 degrees C and at a hydraulic retention time (HRT) of 24 hrs. The membrane used was a ceramic membrane with an ‘‘outside-in’’ flow mode and consisted of 22 open fibres with an inner diameter of approximately 2 mm. The COD removal rate increased from an average value of 62–79% while ammonia removal efficiency decreased from 75 to 60% with gradual increase in BOD. Furthermore, a high BOD removal efficiency (97–99%) was also observed. This clearly indicates that thermophilic system is highly suitable for COD and BOD removal especially at elevated organic loading. However, the system does not favor high nitrogen content wastewaters as the ammonia removal efficiency dropped with increasing BOD/COD ratio. Similar trends were found in TKN analysis as well. However, this system could serve as a pretreatment in removing ammonia. The concentrations of soluble and bound extra-cellular polymeric substances (EPS) found in thermophilic MBR were higher when compared to the corresponding concentrations in a mesophilic MBR, which led to a higher rate of fouling in the thermophilic membrane.

Pretreatment of seawater for biodegradable organic content removal using membrane bioreactor

Reverse osmosis (RO) is currently one of the most prevalent methods used for seawater desalination. During the past four decades, the research anddevelopment has reduced the energy consumption from about 20 to 4 kWh/m3, while improvements in membrane science has led to a 20-fold increase in the specific membrane flux. Nevertheless, research is still underway to reduce the operation and maintenance problems and thus improve the performance of RO systems. The most important maintenance problem associated with RO operation is the membrane fouling, especially biological fouling (biofouling). This work focuses on the aspects to eliminate biofouling in RO membranes, by adopting a proper pretreatment system. The experimental results revealed that fluidized bed biological granular activated carbon, at 15 min empty bed contact time (with dissolved organic carbon, DOC concentration of 6–8 mg/L) can be utilized effectively to remove nearly 100% biodegradable DOC from seawater. Continuous experiments of membrane bioreactor (MBR) have been conducted concomitantly to gain insight into the long-term effects of MBR on biodegradable organic content removal and biofouling control. The results show that MBR system produced better effluent with 78% DOC removal and quasi-total biodegradable DOC removal. Dissolved oxygen was not a limiting factor for the DOC degradation. Short-term experimental runs were conducted with RO membrane using both pretreated and non-pretreated seawater. The results showed that filtrate from MBR yielded the highest permeate flux improvement, which was approximately 300% compared with non-pretreated seawater.

Biological treatment of oily wastewater from gas stations by membrane bioreactor

In many Asian countries, rapid industrialization and urbanization has led to an increased number of cars, making wastewater from gas stations an important issue of concern in urban environment. This wastewater is characterized by high concentration of oil-water emulsion, which cannot be effectively removed by a conventional gravity separator. An experimental investigation on the treatability of oily wastewater from gas stations using a membrane bioreactor (MBR) system revealed that MBR system could achieve good removal efficiency with stability against shock loading. Optimum operating conditions were found to be at a hydraulic retention time of 4 h and an oil-loading rate of 1.8 kg oil m^sup -3^.d^sup -1^. It was anticipated that adding powdered activated carbon (PAC) in the MBR could help to adsorb the oils. However, operating the MBR with only microbial flocs has an advantage over adding PAC particles into the MBR, since the former condition could provide a prolonged cycle of filtration with a relatively lesser increase in transmembrane pressure.

Performance of an oxidation ditch retrofitted with a membrane bioreactor during the start-up

The objective of this study is to elucidate the full-scale characteristics of an oxidation ditch (OD) retrofitted with a membrane bioreactor (MBR). Domestic wastewater entering an oxidation ditch at a flow rate of 86 m3/d was directed to a MBR retrofitted into the original secondary sedimentation tank. The MBR contained flat sheet membranes. The data collected for 2 months during the start-up of the system showed that pH was maintained at 7.2 and 6.7 in OD and MBR, respectively. Dissolved oxygen (DO) in MBR remained stable at 7.8 mg/L, while fluctuated in OD. The mixed liquor suspended solids (MLSS) in the OD remained steady at a concentration about 1000 mg/L, but it was gradually building up from 500 mg/L to 2400 mg/L in the MBR during this period. Measurements of carbohydrate and protein were made by extracting the extra cellular polymeric substances (EPS) with sodium hydroxide (NaOH) from the mixed liquor obtained from both OD and MBR. Carbohydrate was predominant in the EPS and the ratios between carbohydrate and protein converged to fixed values from the fourth week; in this case the ratio was 4.5 for OD and 5 for MBR. The variation in EPS contents showed similar trends in both OD and MBR. The integrated treatment facility removed ammonia, COD and BOD at 100, 91.6 and 97.0%, respectively. However, efficiency of nitrate and phosphate removal has not been realized yet.