Unravelling capability of two-stage thermophilic anaerobic membrane bioreactors for high organic loading wastewater: Effect of support media addition and irreversible fouling.

This study investigated the effects of adding polyvinyl alcohol (PVA) beads on the performance of methanogenic reactors and the fouling behavior of a two-stage thermophilic anaerobic membrane bioreactor (ThAnMBR) for treating wastewater at a feed chemical oxygen demand (COD) of 10 g/L. The PVA-added methanogenic reactor exhibited stable operation performance and offered a relatively low volatile fatty acid concentration effluent with a higher COD removal than the system without PVA addition. The predominant microbial communities in both methanogenic reactors were similar and were assigned to the genus Methanosaeta, followed by Clostridia, which was the predominant genus in the hydrolytic reactor. Ultrafiltration in the PVA-added system offered higher effluent quality and lower fouling resistance. The system was able to operate with hydraulically removable fouling, without any chemical cleaning requirements; however, an elevated flux caused the system to suffer from hydraulically irreversible fouling. PVA beads exhibit their structural stability over long-term operation.

Orbitrap mass spectrometry for the molecular characterization of water resource recovery from polluted surface water using membrane bioreactor.

The increasing organic contamination of surface water hinders the conventional tap water treatment process. Membrane bioreactors (MBRs) are a promising alternative technology for recovering water from polluted surface water. In this study, the composition changes of dissolved organic matters (DOMs) in MBR and ultraviolet/ozone (UV/O3)-MBR systems for polluted surface water treatment were investigated using Orbitrap mass spectrometry analysis with unknown screening. The intense DOM ions within a mass-to-charge ratio range of 100-500 was detected, and 2340 molecular formulae from 5743 peaks were assigned to the two systems. The most abundant components were formulae with C, H, O, N, and CHO only classes. The highest formulae decrease including CHO, CHON, CHOS, and CHONS were attributed to the bio-carrier used in both systems. Results showed that bioprocess was the main contributor in the DOM reduction, and the integration of UV/O3 into the MBR improved the DOM composition changes. Biodegradable components with low O/C ratio in the CHO and CHON classes remarkably increased in the UV/O3-MBR system. The integration of UV/O3 as a polishing step in the recirculation stream of MBR system was effective in improve the DOM removal.

Microplastics contamination in different trophic state lakes along the middle and lower reaches of Yangtze River Basin.

Microplastics can enter freshwater lakes through many sources. They can act as carriers to adsorb bacteria, virus, or pollutants (e.g., heavy metal and toxic organic compounds) that threaten human health through food chain. Microplastics can exist in surface water and sediments in freshwater lakes after they enter the lakes through discharge points. Wastewater discharge is the main cause of lake eutrophication and is the main emission source of microplastics. The correlation between lake trophic state and microplastic abundance has been rarely reported. This study investigated the microplastic contamination in surface water and sediments of 18 lakes along the middle and lower reaches of the Yangtze River Basin in the period of August-September 2018. The correlation between lake trophic state and microplastic abundance in surface water and sediments was investigated and discussed. The microplastic abundance in surface water was approximately two orders of magnitude lower than that in sediments in all 18 lakes. Hong Lake had the highest microplastic abundance in surface water sample, and Nantaizi Lake had the highest microplastic abundance in sediment sample. The dominant microplastic shape was fiber of 93.81% in surface water sample and 94.77% in sediment sample. Blue-colored microplastics were dominant in nearly all lakes in surface water sample (around 40%-60%) and sediment sample (around 60%-80%), followed by purple- and green-colored ones. The microplastics size <1 mm was dominant in surface water sample (around 40%-60%) and sediment sample (around 50%-80%). The dominant material was polypropylene in surface water sample (around 60%-80%) and sediment sample (around 40%-60%).

Effect of PVA-gel filling ratio in attached growth membrane bioreactor for treating polluted surface water.

Surface water has been facing increasing loads of various types of organic contamination due to human activities. Attached growth membrane bioreactor (aMBR) has been reported as a promising approach in treating polluted surface water. By using bio-carrier to provide biodegradation and utilize organic pollutants as substrates, aMBR was able to integrate biodegradation and physical rejection in one system. The filling ratio of polyvinyl alcohol gel (PVA-gel), which is an important bioprocess contributor in an aMBR system, was analyzed by batch test and lab-scale aMBR in this study. Batch test with various filling ratios (2%, 5%, 10%, 15% and 30%) were carried out. Oxygen uptake rate (OUR) and specific oxygen uptake rate were used for the comparison of bioactivities. Five percent filling ratio had the highest OUR results of 3.6 mg/L h obtained from the batch test. The chosen filling ratios were tested in a lab-scale aMBR system with hydraulic retention time (HRT) of 1, 2, 2.5 and 3 h. Results shown that at HRT 2.5 h, the aMBR system had the lowest membrane fouling. PVA-gel was able to reject more organic matters than a naturally immobilized membrane bioreactor system, and thus mitigated membrane fouling in the aMBR system.

Performances study of UV/O3-aMBR recirculation system in treating polluted surface water.

This study used UV/O3-aMBR system for treating polluted surface water with CODMn around 10 mg/L, to improve the removal of non-biodegradable components. UV/O3 was used in the recirculation stream, partially treating the recalcitrant in aMBR permeate to improve its biodegradability, and then send back to aMBR for biodegradation. Removal performance of UV/O3-aMBR system with recirculation ratio 20, 40, 60 and 80% was tested and compared. The removal of CODMn, UV254 and NH3-N increased with the increment of recirculation ratio. UV/O3-aMBR system has higher recalcitrant removal performance and less membrane fouling. The fluorescent dissolved organic matter (FDOM) was largely reduced in UV/O3-aMBR system, and the system hydrophilicity was higher than aMBR system. The Modified Stover Kincanoon model was able to describe UV/O3-aMBR system; and has higher Umax than aMBR system. UV/O3-aMBR can be develop as an effective technology in improving recalcitrant removal in polluted surface water treatment.

Performance evaluation of attached growth membrane bioreactor for treating polluted surface water.

Attached growth membrane bioreactor (aMBR) process was investigated for treating polluted surface water with CODMn around 10mg/L of raw water. Lab scale reactors, aMBR with 15% PVA-gel as carrier and conventional membrane filtration reactor (MF) were tested in parallel. aMBR achieved two times higher CODMn removal than MF system. Ammonia removal occurred almost completely in both MF and aMBR system - around 94% and 96%, respectively. Permeate turbidity was almost totally removed while UV254 removal was around 15% in MF and 20% in aMBR system. aMBR system largely mitigated membrane fouling and prolonged the system operation time. Results showed 2h hydraulic retention time provided relatively higher removal efficiency and stable operation performance. Modified Stover Kincannon model was able to match the aMBR system.

Thermophilic co-digestion feasibility of distillers grains and swine manure: effect of C/N ratio and organic loading rate during high solid anaerobic digestion (HSAD).

Anaerobic co-digestion of high solids containing distillers grains and swine manure (total solids, 27 +/- 2% and 18 +/- 2%, respectively) was evaluated in this study to assess the effect of C/N ratio and organic loading rate (OLR). Feed mixture was balanced to achieve a C/N ratio of 30/1 by mixing distillers grains and swine manure. Pilot-scale co-digestion of distillers grains and swine manure was carried out under thermophilic conditions in the continuous mode for seven different OLRs from R1 to R7 (3.5, 5, 6, 8, 10, 12 and 14 kg VS/m3 day) under high solid anaerobic digestion. The methane yield and volatile solid (VS) removal were consistent; ranging from 0.33 to 0.34 m3CH4/kg VS day and 50-53%, respectively, until OLR 8 kg VS/m3 day. After which methane yield and VS removal significantly decreased to 0.26 m3 CH4/kg VS day and 42%, respectively, when OLR was increased to 14 kg VS/m3 day. However, during operation, at OLR of 10 kg VS/m3 day, the methane yield and VS removal increased after the 19th day to 0.33 m3 CH4/kg VS day and 46%, respectively, indicating that a longer acclimatization period is required by methanogens at a higher loading rate.

Influence of biofilm carriers on membrane fouling propensity in moving biofilm membrane bioreactor.

In moving biofilm membrane bioreactor (MB-MBR) sponge carriers for biofilm growth were coupled with conventional submerged membrane bioreactor (C-MBR). This study compared the fouling propensity of C-MBR with MB-MBR and investigated factors affecting fouling variations in both the systems. Membrane fouling tendencies were monitored in terms of trans-membrane pressure (TMP) and the fouling characterization included membrane fouling resistances in situ and specific cake resistance (SCR) in batch filtration cell. Comparison of TMP profiles depicted prolong filtration periods in MB-MBR. Cake layer resistance (R(c)), pore blocking resistance (R(p)) as well as SCR were higher in C-MBR. The study reveals that hybrid biomass in MB-MBR creates relatively more porous cake structure in the absence of filamentous bacteria which were found in abundance in C-MBR. Filamentous bacteria were also responsible for the release of high concentration of carbohydrates in the form of soluble extra polymeric substance (EPS) contributing to higher R(p) in C-MBR.

Effect of powdered activated carbon (PAC) and cationic polymer on biofouling mitigation in hybrid MBRs.

In this study, the influence of powdered activated carbon (PAC) and cationic polymer (MPE50) was investigated on the fouling propensity in hybrid MBRs. Three laboratory scale MBRs were operated simultaneously including MBR(Control), MBR(PAC), and MBR(Polymer). Optimum dosages of PAC and polymer to the MBR(PAC) and MBR(Polymer), respectively were determined using jar tests. It was found that the MBR(PAC) exhibited low fouling tendency and prolonged filtration as compared to the other MBRs. Improved filtration in MBR(PAC) was attributed to the flocculation and adsorption phenomena. The effective stability of the biomass by PAC in the form of biological activated carbon (BAC) was verified by the increase in mean particle size. The BAC aided sludge layer exhibited porous cake structure resulting in the prolong filtration. However, both the membrane hybrid systems revealed effective adsorption of organic matter by 40% reduction in the soluble EPS concentration.

Sustainable landfilling in tropical conditions: comparison between open and closed cell approach.

Two landfill test cells were constructed in a tropical climate using locally available low-cost materials. One cell was operated without a cover on the municipal solid waste to simulate 'open landfill' conditions and the other cell was covered to create 'closed landfill' conditions. Both test cells were monitored over a period of 290 days under rainy, dry and artificial wetting conditions. Due to the relatively high compaction density of waste in the closed test cell, the substrate settlement was gradual and comparatively lower than in the open test cell. Multiple top covers in the closed test cell resulted in significant run-off of incident precipitation during the rainy season, which delayed the waste stabilization and subsequently produced a lesser volume of leachate. On the other hand, operation of the open test cell was found to be advantageous in terms of leachate management and substrate settlement along with waste stabilization pattern. Infiltration of rain-water into the waste mass leached out the maximum organic pollutants and oxidized the nitrogen content, which is deemed to be a benefit of operating an open cell landfill under tropical conditions. Artificial wetting during dry periods by recirculation of stored leachate notably accelerated the waste stabilization and secondary substrate settlement in the open test cell. The continuous monitoring of ground-water quality from the site showed only seasonal variations.

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.

Co-disposal of electronic waste with municipal solid waste in bioreactor landfills.

Three pilot scale lysimeters were adopted to evaluate the stability pattern and leaching potential of heavy metals from MSW landfills under the E-waste co-disposed condition. One lysimeter served as control and solely filled with MSW, whereas the other two lysimeters were provided with 10% and 25% of E-waste scraps (% by weight), respectively. The reactors were monitored over a period of 280 days at ambient settings with continuous leachate recirculation. Stabilization pattern of carbon appears to be more than 50% in all the three lysimeters with irrespective of their operating conditions. Iron and zinc concentrations were high in leachate during bioreactor landfill operation and correlating with the TCLP leachability test results. In contrast, Pb concentration was around <0.6 mg/L, but which showed maximum leaching potential under TCLP test conditions. But, no heavy metal accumulation was found with leachate recirculation practices in lysimeters. Mobility of the metal content from the E-waste was found to be amplified with the long term disposal or stabilization within landfills. The results showed that the TCLP test cannot be completely reliable tool for measuring long-term leachability of toxic substances under landfill condition; rather landfill lysimeter studies are necessary to get the real scenario.

Healthcare waste management in Asia.

The risks associated with healthcare waste and its management has gained attention across the world in various events, local and international forums and summits. However, the need for proper healthcare waste management has been gaining recognition slowly due to the substantial disease burdens associated with poor practices, including exposure to infectious agents and toxic substances. Despite the magnitude of the problem, practices, capacities and policies in many countries in dealing with healthcare waste disposal, especially developing nations, is inadequate and requires intensification. This paper looks upon aspects to drive improvements to the existing healthcare waste management situation. The paper places recommendation based on a 12 country study reflecting the current status. The paper does not advocate for any complex technology but calls for changes in mindset of all concerned stakeholders and identifies five important aspects for serious consideration. Understanding the role of governments and healthcare facilities, the paper also outlines three key areas for prioritized action for both parties - budget support, developing policies and legislation and technology and knowledge management.

Prediction of membrane fouling in MBR systems using empirically estimated specific cake resistance.

The focus of this study was to empirically estimate the specific cake resistance (SCR) by the variation in shear intensity (G) in four laboratory-scale MBRs. The control reactor (MBR(0)) was operated with aeration only while other MBRs (MBR(150), MBR(300) and MBR(450)) were operated with aeration and mechanical mixing intensities of 150, 300 and 450 rpm, respectively. It was found that the SCR was strongly correlated (R(2)=0.99) with the fouling rates in the MBRs. Moreover, the contribution of cake resistance (R(c)) to the total hydraulic resistance (R(t)) was predominant compared to the irreversible fouling resistance (R(f)). On this basis, the cake filtration model was selected as a predictive tool for membrane fouling. This model was modified by replacing the SCR with its empirical shear intensity relationship. The modified model can predict the fouling rate for a given shear intensity (G) within 80 and 250 s(-1) in a MBR system.

Hydrogenotrophic denitrification of highly saline aquaculture wastewater using hollow fiber membrane bioreactor.

A hydrogenotrophic denitrification system with a hollow fiber membrane was evaluated for treating and recycling synthetic aquaculture wastewater. Hollow fibers ensured bubble-less diffusion of hydrogen and subsequent removal of nitrate from the first bioreactor. The second aerobic reactor was used for biomass filtration and removal of organic matter. Nitrate and organic matter expressed as dissolved organic carbon were 50 mgl(-1) and 20 mgl(-1), respectively, in the inlet. Acclimatization of hydrogenotrophic bacteria to 10, 20 and 30 ppt of salinity was also observed. Optimum hydraulic retention time and denitrification rate corresponding to these salinities were 3, 5 and 6 h and 366.8, 226.2 and 193.2 gm(-3) day(-1), respectively.

Assessment of Hg contamination and exposure to miners and schoolchildren at a small-scale gold mining and recovery operation in Thailand.

Gold extracted by Hg-amalgamation process, which can cause both health and environmental problems, is widespread in South East Asia including Myanmar, Laos, Cambodia, and Thailand. Small-scale gold mining operations have been carried out since the year 2000 in Phanom Pha District, Phichit Province, Thailand. Since no data is available for evaluating Hg exposure, an investigation of mercury (Hg) contamination and exposure assessment was carried out at this mine site. Environmental monitoring illustrated the total Hg in water was as high as 4 microg/l while Hg in sediment ranged between 102 to 325 microg/kg dry weight. Both Hg deposition from the air (1.28 microg/100 cm(2)/day) and concentration in surface soil (20,960 microg/kg dry weight) were elevated in the area of amalgamation. The potential of Hg exposure to miners as well as to schoolchildren was assessed. The concentrations of Hg in urine of 79 miners who were directly (group I) or indirectly (group II) involved in the gold recovery operation were 32.02 and 20.04 microg/g creatinine, respectively, which did not exceed regulatory limits (35 microg/g creatinine). Hair Hg levels in both groups (group I and group II) also were not significantly higher than the non-exposed group. In terms of risk factors, gender and nature of food preparation and consumption were the two significant variables influencing the concentration of Hg in urine of miners (P < 0.05). A hazard quotient (HQ) was estimated based on the inorganic Hg exposure of individual miners. The HQ values of group I were in a range 16 to 218 times higher than the safety level set as 1. By comparison the group II HQ index was very low (0.03-0.39). The miners in group I who worked and ate food from this area experienced potentially high exposure to Hg associated with the mining process. In a second Hg exposure assessment, a group of 59 schoolchildren who attended an elementary school near the gold mine site was evaluated for Hg exposure. A slightly higher Hg urine concentration was detected in group I and group II (involved and not involved in gold recovery) at average levels of 15.82 and 9.95 microg/g creatinine, respectively. The average Hg values for both groups were below the established levels indicating no risk from Hg intake. Average Hg hair level in all schoolchildren (0.93 microg/g) was not significantly higher than reference group. There were two variables (gender and personal hygiene) which affected the concentration of Hg in urine of schoolchildren (P < 0.05). The result (HQ) also suggested that schoolchildren were not at risk (< 1). Schoolchildren involved in gold mining activities showed some indirect exposure to Hg from the adults working in mining area.

Municipal solid waste management in Thailand and disposal emission inventory.

The increasing municipal solid waste (MSW) generation along with the high fraction of organic waste and a common disposal of open dumping is the current scenario in many areas in Thailand. As a response to this problem, the country's Pollution Control Department (PCD) aims to reduce the MSW generation rate to less than 1 kg/capita/day, increase the collection efficiency, and improve the recovery of recyclables. For many years, more than 60% of the solid waste disposal system in Thailand has been carried out by open dumping. According to the survey conducted by this study, in 2004 there were 425 disposal sites (95 landfills; 330 open dumps) in Thailand and an estimated methane emission of 115.4 Gg/year was generated based on this practice. It has been estimated that the anticipated methane emission in Thailand will rise from 115.4 Gg/year to 118.5 Gg/year if the largest open dumpsites in provinces with no existing landfill are upgraded to sanitary landfill; and it will increase to 193.5 Gg/year if the existing sanitary landfill is upgraded to integrated waste management facilities. Moreover, Bangkok metropolitan have the highest methane emission (54.83 Gg/year) among all the regions in Thailand. The methane emission forecast of 339 Gg/year by 2020 (based on LandGEM methodology) provides a stimulus to create a comprehensive plan to capture and utilize methane as an energy source.

Anaerobic digestion of municipal solid waste as a treatment prior to landfill.

Anaerobic digestion of organic fraction of municipal solid waste was conducted in pilot-scale reactor based on high-solid combined anaerobic digestion process. This study was performed in two runs. In Run 1 and Run 2, pre-stage flushing and micro-aeration were conducted to determine their effect in terms of enhancing hydrolysis and acidification in ambient condition. In Run 2, after pre-stage, the methane phase (methanogenesis) was started-up after pH adjustment and inoculum addition in mesophilic condition. Acidified leachate produced in pre-stage was used for percolation during active methane phase. At the end of methane phase, air flushing was conducted before unloading the digesters. Hydrolysis and acidification yield of 140 g C/kg TS and 180 g VFA/kg TS were achieved, respectively in pre-stage. Micro-aeration exhibited an equivocal result in terms of enhancing hydrolysis/acidification; however it showed a positive effect in methane phase performance and this needed further investigation. Leachate percolation during methane phase showed an enhanced methanization when compared to the reactors without leachate percolation. After 60 days, 260 l CH(4)/kg VS was obtained. Based on the waste methane potential, 75% biogas conversion and 61% VS degradation were achieved.

Removal of inhibitory phenolic compounds by biological activated carbon coupled membrane bioreactor.

Phenolic compounds cause problems for conventional treatments due to their toxic and inhibitory properties. This work investigated the treatability of phenolic compounds by using two membrane-bioreactor systems, namely: activated sludge coupled with MBR (AS-MBR) and biological granular activated carbon coupled with MBR (BAC-MBR). Initially, the system was fed with phenol (500 mg/L) followed by adding 2,4-dichlorophenol (2,4-DCP). Phenol, 2,4-DCP, TOC and COD removal were higher than 98.99% when the organic load ranged between 1.80 and 5.76 kg/m3.d COD. In addition to MBR system development, removal mechanisms were also investigated. Relatively low values of phenol adsorption of GAC and biomass, and high maximum substrate removal rates obtained from a biokinetic experiment, proved that the removals were mainly due to biodegradation. Analysis of sludge indicated a significant difference in the sludge characteristics of the two reactors. The high EPS content in BAC-MBR led to higher viscosity and poor sludge settling properties. The relationship between sludge properties and EPS components revealed that settleability had no direct correlation with EPS, though it was better correlated to protein/carbohydrate ratios.