Effects of Low Oxygen Dosages on an Anaerobic Membrane Bioreactor, Simulating the Oxygen Load in an Anaerobic Digester-Dissolved Air Flotation (AD-DAF) System.

This study reports the effects of microaeration on a laboratory-scale AnMBR (MA-AnMBR) fed with synthetic concentrated domestic sewage. The imposed oxygen load mimics the oxygen load coming from a dissolved air flotation (DAF) unit, establishing an anaerobic digester-DAF (AD-DAF) combination with sludge recycling. Results showed a reduced COD concentration in the MA-AnMBR permeate compared with the AnMBR permeate, from 90 to 74 mgCOD L-1, and a concomitant 27% decrease in biogas production. The MA-AnMBR permeate ammonium (NH4+) concentration increased by 35%, to 740 mgNH4+-N L-1, indicating a rise in the hydrolytic capacity. Furthermore, the MA-AnMBR biomass seemingly adapted to an increased oxygen load, which corresponded to 1% of the influent COD load (approximately 55 mLO2 d-1). Concomitantly, an increase in the superoxide dismutase activity (SOD) of biomass was detected. Meanwhile, negligible changes were observed in the specific methanogenic activity (SMA) of the microaerated biomass that was subjected to an oxygen load equivalent to 3% of the influent COD load in batch tests. The obtained results showed that an AD-DAF system could be a promising technology for treating concentrated domestic wastewater, improving sewage sludge hydrolysis, and overall organic matter removal when compared to an AnMBR.

Performance of Anaerobic Membrane Bioreactor (AnMBR) with Sugarcane Bagasse Ash-based Ceramic Membrane treating Simulated Low-strength Municipal Wastewater: Effect of Operation Conditions.

This study assesses the performance of waste sugarcane bagasse ash (SBA)-based ceramic membrane in anaerobic membrane bioreactor (AnMBR) treating low-strength wastewater. The AnMBR was operated in sequential batch reactor (SBR) mode at hydraulic retention time (HRT) of 24 h, 18 h, and 10 h to understand the effect on organics removal and membrane performance. Feast-famine conditions were also examined to evaluate system performance under variable influent loadings. An average removal of >90% chemical oxygen demand (COD) was obtained at each HRT and starvation periods up to 96 days did not significantly affect removal efficiency. However, feast-famine conditions affected extracellular polymeric substances (EPS) production and consequently the membrane fouling. EPS production was high (135 mg/g MLVSS) when the system was restarted at 18 h HRT after shutdown (96 days) with corresponding high transmembrane pressure (TMP) build-up; however, the EPS content stabilized at ~60-80 mg/g MLVSS after a week of operation. Similar phenomenon of high EPS and high TMP was experienced after other shutdowns (94 and 48 days) as well. Permeate flux was 8.8±0.3, 11.2±0.1 and 18.4±3.4 L/m2 h at 24 h, 18 h and 10 h HRT, respectively. Filtration-relaxation (4 min - 1 min) and backflush (up to 4 times operating flux) helped control fouling rate. Surface deposits (that significantly attributed to fouling) could be effectively removed by physical cleaning, resulting in nearly complete flux recovery. Overall, SBR-AnMBR system equipped with waste-based ceramic membrane appears promising for treatment of low-strength wastewater with disruptions in feeding. Supplementary Information: The online version contains supplementary material available at 10.1007/s11270-023-06173-3.

Phytochemicals from fruit and vegetable waste generated in hotels: Optimization of recovery procedure and potential for value-addition.

Fifteen star-category hotels in the National Capital Region of India were surveyed to assess the mixed fruit and vegetable waste generated. Based on the survey, a model mixed waste was prepared and used to identify the optimal procedure for recovery of bioactive phytochemicals and Trolox equivalent antioxidant capacity (TEAC) followed by preliminary identification of phytochemical constituents. The optimization procedure was done over (i) level I focusing on sample type (fresh, oven dried, vacuum dried), extraction technique (maceration, ultrasound assisted extraction), removal of interfering components by treatment with dichloromethane (DCM) and extraction in different solvents, and (ii) level II focusing on solvent concentration and extraction time, in both non DCM and DCM treated samples. The model mixed waste consisted of peels of pineapple, papaya, potato, pomegranate, apple, onion and citrus. The optimal conditions for recovery of phytochemicals and TEAC were non DCM treated vacuum dried samples subjected to ultrasonic assisted extraction for 60 min using âˆ¼ 63% acetone. This resulted in recovery of appreciable amounts of total extractable phytochemicals consisting of polyphenols and flavonoids as the major components with relatively smaller amounts of flavones and flavanols. High TEAC values were obtained with both aqueous phase (ABTS) and organic phase (DPPH) assays. Preliminary investigation revealed the presence of various high-value compounds particularly gallic acid, ferulic acid, rutin and catechin in the phytochemicals extract. Consequently, there is significant potential to recover value-added phytochemicals from mixed fruit and vegetable waste from hotels contributing towards a circular bioeconomy.

Are pharmaceuticals removal and membrane fouling in electromembrane bioreactor affected by current density?

Pharmaceutical active compounds (PhACs) have been detected at significant concentrations in various natural and artificial aquatic environments. In this study, electro membrane bioreactor (eMBR) technology was used to treat simulated municipal wastewater containing widely-used pharmaceuticals namely amoxicillin (AMX), diclofenac (DCF) and carbamazepine (CBZ). The effects of varying current density on the removal of PhACs (AMX, DCF and CBZ) and conventional pollutants (chemical oxygen demand (COD), dissolved organic carbon (DOC), humic substances, ammonia nitrogen (NH4-N), nitrate nitrogen (NO3-N) and orthophosphate (PO4-P) species) were examined. High COD and DOC removal efficiencies (~100%) were obtained in all the experimental runs regardless of applied current density. In contrast, enhanced removal efficiencies for AMX, DCF and CBZ were achieved at high current densities. Membrane fouling rate in eMBR with respect to conventional MBR was reduced by 24, 44 and 45% at current densities of 0.3, 0.5 and 1.15 mA/cm2, respectively. The mechanism for pharmaceutical removal in this study proceeded by: (1) charge neutralization between negatively-charged pharmaceutical compounds and positive electro-generated aluminium coagulants to form larger particles and (2) size exclusion by membrane filtration.

Applicability of the electrocoagulation process in treating real municipal wastewater containing pharmaceutical active compounds.

In this study, the viability of using electrocoagulation process as a method for pharmaceuticals removal from real municipal wastewater was demonstrated. Batch experimental runs were performed using a simple laboratory scale electrochemical reactor with aluminium and stainless steel as anode and cathode, respectively. Diclofenac (DCF), carbamazepine (CBZ) and amoxicillin (AMX) were selected as representative of pharmaceuticals frequently detected in the aquatic environment. The effects of varying experimental parameters namely current density (0.3, 0.5 1.15 and 1.8 mA cm-2), initial pharmaceutical concentration (0.01, 4 and 10 mg L-1), electrolysis duration (3, 6 and 19 h) and application mode (continuous vs. intermittent) on pharmaceutical removal efficiencies were evaluated. High pharmaceutical abatement was recorded at elevated current density and prolonged electrolysis duration due to additional electro-generated coagulant species in solution.

Forward Osmosis in Wastewater Treatment Processes.

In recent years, membrane technology has been widely used in wastewater treatment and water purification. Membrane technology is simple to operate and produces very high quality water for human consumption and industrial purposes. One of the promising technologies for water and wastewater treatment is the application of forward osmosis. Essentially, forward osmosis is a process in which water is driven through a semipermeable membrane from a feed solution to a draw solution due to the osmotic pressure gradient across the membrane. The immediate advantage over existing pressure driven membrane technologies is that the forward osmosis process per se eliminates the need for operation with high hydraulic pressure and forward osmosis has low fouling tendency. Hence, it provides an opportunity for saving energy and membrane replacement cost. However, there are many limitations that still need to be addressed. Here we briefly review some of the applications within water purification and new developments in forward osmosis membrane fabrication.

High strength distillery wastewater treatment by a PAC-MBR with low PAC dosage.

Augmentation of membrane bioreactors (MBRs) with activated carbon is established to offer several operational advantages. This work investigates the influence of low dosing (2 g/L) of powdered activated carbons (PACs) with different characteristics on the performance of MBR treating high strength molasses distillery wastewater containing difficult-to-biodegrade recalcitrant components. Two MBRs, augmented with different PACs, were operated in parallel over a period of 240 days and their performance monitored in terms of biomass growth, reduction in chemical oxygen demand (COD), sludge properties like extracellular polymeric substances content, filterability, and morphology. Removal of organics and coloring matter by adsorption, biodegradation and membrane filtration was estimated. Although adsorptive removal of color and COD is influenced by the properties of the PAC used, the performance of the PAC-MBRs was independent of PAC properties. Both PACs preferentially adsorbed the low molecular weight components in distillery wastewater. Retention by the membrane filter with the secondary cake layer contributed to reduction in color and COD of treated effluent. The findings indicate that low dosing with PAC adsorbing low molecular weight organics has a limited role in PAC-MBR treating distillery wastewater.

Covalently Immobilized Laccase for Decolourization of Glucose-Glycine Maillard Products as Colourant of Distillery Wastewater.

Maillard reaction products like melanoidins are recalcitrant, high-molecular-weight compounds responsible for colour in sugarcane molasses distillery wastewater. Conventional biological treatment is unable to break down melanoidins, but extracellular laccase and manganese peroxidase of microbial origin can degrade these complex molecules. In this work, laccase was covalently immobilized on alumina pellets activated with aminopropyltriethoxysilane (APTES). The immobilization yield was 50-60 %, and the enzyme activity (886 U/L) was 5-fold higher compared to the soluble enzyme (176 U/L). The immobilized enzyme also showed higher tolerance to pH (4-6) and temperature (35-60 °C), as well as improved storage stability (49 days) and operational stability (10 cycles). Degradation of glucose-glycine Maillard products using immobilized laccase led to 47 % decolourization in 6 h at pH 4.5 and 28 °C. A comprehensive treatment scheme integrating enzymatic, microbial and membrane filtration steps resulted in 90 % decolourization.

Integrated treatment of molasses distillery wastewater using microfiltration (MF).

To achieve zero-liquid discharge, high pressure reverse osmosis (RO) of effluent is being employed by molasses based alcohol distilleries. Low pressure and thus less energy intensive microfiltration (MF) is well established for particulate separation but is not suitable for removal of dissolved organics and color. This work investigates two schemes incorporating MF for molasses distillery wastewater (a) chemical coagulation followed by treatment in a membrane bioreactor (MBR) using MF and (b) electrocoagulation followed by MF. The performance was assessed in terms of COD and color reduction; the conversion of the generated sludge into a zeolite desiccant was also examined. A comparison of the schemes indicates electrocoagulation followed by MF through a 0.1 µm membrane to be most effective. By hydrothermal treatment, electrocoagulated sludge can be transformed into a porous NaX zeolite with a surface area of 86 m(2)/g, which is comparable to commercial desiccants.

Treatment of nitrate-rich water in a baffled membrane bioreactor (BMBR) employing waste derived materials.

Nitrate removal in submerged membrane bioreactors (MBRs) is limited as intensive aeration (for maintaining adequate dissolved oxygen levels and for membrane scouring) deters the formation of anoxic zones essential for biological denitrification. The present study employs baffled membrane bioreactor (BMBR) to overcome this constraint. Treatment of nitrate rich water (synthetic and real groundwater) was investigated. Sludge separation was achieved using ceramic membrane filters prepared from waste sugarcane bagasse ash. A complex external carbon source (leachate from anaerobic digestion of food waste) was used to maintain an appropriate C/N ratio. Over 90% COD and 95% NO3-N reduction was obtained. The bagasse ash filters produced a clear permeate, free of suspended solids. Sludge aggregates were observed in the reactor and were linked to the high extracellular polymeric substances (EPS) content. Lower sludge volume index (40 mL/g compared to 150 mL/g for seed sludge), higher settling velocity (47 m/h compared to 10 m/h for seed sludge) and sludge aggregates (0.7 mm aggregates compared to <0.2 mm for seed sludge) was observed. The results demonstrate the potential of waste-derived materials viz. food waste leachate and bagasse ash filters in water treatment.

Performance enhancement with powdered activated carbon (PAC) addition in a membrane bioreactor (MBR) treating distillery effluent.

This work investigated the effect of powdered activated carbon (PAC) addition on the operation of a membrane bioreactor (MBR) treating sugarcane molasses based distillery wastewater (spentwash). The 8L reactor was equipped with a submerged 30 microm nylon mesh filter with 0.05 m(2) filtration area. Detailed characterization of the commercial wood charcoal based PAC was performed before using it in the MBR. The MBR was operated over 200 days at organic loading rates (OLRs) varying from 4.2 to 6.9 kg m(-3)d(-1). PAC addition controlled the reactor foaming during start up and enhanced the critical flux by around 23%; it also prolonged the duration between filter cleaning. Operation at higher loading rates was possible and for a given OLR, the chemical oxygen demand (COD) removal was higher with PAC addition. However, biodegradation in the reactor was limited and the high molecular weight compounds were not affected by PAC supplementation. The functional groups on PAC appear to interact with the polysaccharide portion of the sludge, which may reduce its propensity to interact with the nylon mesh.

Effect of PAC addition on sludge properties in an MBR treating high strength wastewater.

This paper examines the sludge characteristics in a submerged membrane bioreactor (MBR) operated on a high strength wastewater from an alcohol distillery. Two membrane bioreactors, each with a 30 microm mesh filter, were investigated with and without addition of powdered activated carbon (PAC). Experiments were conducted with varying organic loading rates ranging from 3.4 to 6.9 kgCOD m(-3) day(-1) and the specific oxygen uptake rate (SOUR), sludge volume index (SVI), mixed liquor suspended solids (MLSS), particle size and extracellular polymeric substances (EPS) were monitored over a 180 day period. Respirometric experiments did not show enhancement in microbial activity with PAC supplementation. Addition of PAC decreased the SVI thereby perceptibly improving sludge dewaterability. The sludge particle size, which increased with time, appeared to be independent of PAC addition but was influenced by the aeration intensity. PAC also did not affect the sludge EPS concentration; however, the EPS composition, in terms of protein/carbohydrate (polysaccharide) ratio was altered resulting in a high P/C ratio. FTIR analysis of the sludge samples indicated that the functional groups associated with the sludge polysaccharides appear to be involved in its interaction with PAC.