Production and characterization of β-glucosidase from Aspergillus niger fermentation: Application for organic fraction of municipal solid waste hydrolysis and methane enhancement

The anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) is currently an attractive treatment process with energy production in the form of biogas. Hydrolysis is the rate-limiting step for the anaerobic digestion of solid wastes. Thus, in the present study fungal enzymatic pretreatment of OFMSW was applied to enhance biogas production. Two enzyme cocktails rich on β-glucosidase were produced from submerged fermentation of Aspergillus niger on basal medium using OFMSW as carbon source and urea (Urea cocktail) and Ulva rigida as nitrogen source (Ulva cocktail). Ulva cocktail displayed an important effect on OFMSW solubilization. Therefore, an increase of reducing sugar concentration about 60% was obtained which was in correlation with chemical oxygen demand (COD) increase. The performance of enzymatic pretreatment on anaerobic digestion of OFMSW was studied by conducting biochemical methane potential tests. Results showed that the enzymatic pretreatment improved methane yield of OFMSW even at high solid concentration. High methane yield about 500 ml/g total volatile solid was obtained, which corresponds up to 68% enhancement over the control.     

Performance of an anaerobic baffled reactor and hybrid constructed wetland treating high-strength wastewater in Nepal—A model for DEWATS

Centralized wastewater treatment systems require sophisticated technologies and skilled manpower for their operation and maintenance (O&M). These systems have huge construction as well as O&M costs. Therefore, a Decentralized Wastewater Treatment System (DEWATS) rather than a centralized system might be especially beneficial in developing countries. A model for DEWATS is developed in Nepal with Anaerobic Baffled Reactor (ABR) and hybrid Constructed Wetland (CW). The DEWATS treats high-strength wastewater from 80 households (400 PE). This paper summarizes the performance of the DEWATS from July 2006 to August 2007 in the removal efficiencies of TSS, BOD₅, COD, NH₄–N, TP and FC. The ABR is very effective in the removal of organic pollutants and could achieve TSS removal up to 91%, BOD₅ up to 78% and COD up to 77%. The average removal efficiencies of the DEWATS is 96% TSS, 90% BOD₅, 90% COD, 70% NH₄–N, 26% TP and 98% FC.     

Effect of pre-aeration and inoculum on the start-up of batch thermophilic anaerobic digestion of municipal solid waste

In this study, a short pre-aeration step was investigated as pre-treatment for thermophilic anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). It was found that pre-aeration of 48 h generated enough biological heat to increase the temperature of bulk OFMSW to 60 °C. This was sufficient self-heating of the bulk OFMSW for the start-up of thermophilic anaerobic digestion without the need for an external heat source. Pre-aeration also reduced excess easily degradable organic compounds in OFMSW, which were the common cause of acidification during the start-up of the batch system. Careful consideration however must be taken to avoid over aeration as this consumes substrate, which would otherwise be available to methanogens to produce biogas. To accelerate methane production and volatile solids destruction, the anaerobic digestion in this study was operated as a wet process with the anaerobic liquid recycled through the OFMSW. Appropriate anaerobic liquid inoculum was found to be particularly beneficial. It provided high buffer capacity as well as suitable microbial inoculum. As a result, acidification during start-up was kept to a minimum. With volatile fatty acids (VFAs-acetate in particular) and H₂ accumulation typical of hydrolysis and fermentation of the easily degradable substrates during start-up, inoculum with high numbers of hydrogenotrophic methanogens was critical to not only maximise CH₄ production but also reduce H₂ partial pressure in the system to allow VFAs degradation. In a lab-scale bioreactor, the combined pre-aeration and wet thermophilic anaerobic digestion was able to stabilise the OFMSW within a period of only 12 days. The stabilised inert residual material can be used as a soil amendment product.     

Pretreatment of turkey fat-containing wastewater in coarse sand and gravel/coarse sand bioreactors

Fat, oil and grease in wastewater can be difficult to treat because of their slow decomposition. Traditional pretreatment facilities to remove fat, oil and grease from wastewater are increasingly costly. The hypothesis in this study was that pretreatment of animal fat-containing wastewater in sand and sand/gravel filters facilitates the conversion of slowly degradable organic matter measured as the difference between chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD₅) for subsequent biological treatment. The pretreatment was evaluated using simulated turkey-processing wastewater and coarse sand and sand/gravel filters at a constant hydraulic loading rate of 132 L/m²/day. Two types of fixed media reactors were employed: (i) one set with a varying depth of coarse sand, and (ii) the second was similar but with an additional pea gravel cap. The results indicated that the relative removal of COD was slightly improved in the sand bioreactors with a pea gravel cap irrespective of the depth of coarse sand, but partial conversion to BOD₅ was not consistently demonstrated. Pea gravel may act as a sieve to entrap organic matter including fat globules from the wastewater. Multiple dosing at the same daily loading rate slightly improved the treatment efficiency of the sand bioreactors. The ratios of influent-COD/effluent-COD were always greater than 1.0 following a change in the dosing frequency after a rest period, suggesting that organic matter, specifically fat globules in this case, was retained by the column matrix.     

Biomonitoring of wastewaters in treatment plants using ciliates

The aim of this project has been to study and compare the ciliate populations present in roptating biological reactors treating three different wastewaters. Wastewaters chosen were a maize mill (nejayote), a sugarcane/ethyl alcohol plant (vinasses) and a recycled paper mill (whitewaters). The initial dissolved organic contents, measured as soluble chemical oxygen demand (COD) and biochemical oxygen demand in five days (BOD₅), were 2040±150 mg COD L^–1 and 585±5 mg BOD₅L^–1 for nejayote; 2000±20 mg COD L^–1 and 640±5 mg BOD₅ L^–1 for vinasses and 960±200 mg COD L^–1 and 120±10 mg BOD₅ L^–1 for whitewaters. Results obtained indicate that ciliated protozoa proliferated in the different chambers of each rotating biological reactor (RBR). Saprobity indices, as a quantitative evaluation parameter, indicate that there are no universal species of ciliates associated with specific BOD₅ concentrations. Therefore, the number of species of ciliates present in the effluent indicate qualitatively the efficiency of removal of pollution from the wastewaters during treatment in the rotating biological reactors.     

Partial nitrification and nutrient removal in intermittently aerated sequencing batch reactors treating separated digestate liquid after anaerobic digestion of pig manure

The performance of an intermittently aerated sequencing batch reactor (IASBR) technology was investigated in achieving partial nitrification, organic matter removal and nitrogen removal from separated digestate liquid after anaerobic digestion of pig manure. The wastewater had chemical oxygen demand (COD) concentrations of 11,540 ± 860 mg/L, 5-day biochemical oxygen demand (BOD₅) concentrations of 2,900 ± 200 mg/L and total nitrogen (TN) concentrations of 4,041 ± 59 mg/L, with low COD:N ratios (2.9) and BOD₅:COD ratios (0.25). Synthetic wastewater, simulating the separated digestate liquid with similar COD and nitrogen concentrations but BOD₅ of 11,500 ± 100 mg/L, was also treated using the IASBR technology. At a mean organic loading rate of 1.15 kg COD/(m³ d) and a nitrogen loading rate of 0.38 kg N/(m³ d), the COD removal efficiency was 89.8% in the IASBR (IASBR-1) treating digestate liquid and 99% in the IASBR (IASBR-2) treating synthetic wastewater. The IASBR-1 effluent COD was mainly due to inert organic matter and can be further reduced to less than 40 mg/L through coagulation. The partial nitrification efficiency of 71–79% was achieved in the two IASBRs and one cause for the stable long-term partial nitrification was the intermittent aeration strategy. Nitrogen removal efficiencies were 76.5 and 97% in IASBR-1 and IASBR-2, respectively. The high nitrogen removal efficiencies show that the IASBR technology is a promising technology for nitrogen removal from low COD:N ratio wastewaters. The nitrogen balance analysis shows that 59.4 and 74.3% of nitrogen removed was via heterotrophic denitrification in the non-aeration periods in IASBR-1 and IASBR-2, respectively.     

A comparison study on the high-rate co-digestion of sewage sludge and food waste using a temperature-phased anaerobic sequencing batch reactor system

Assessing contemporary anaerobic biotechnologies requires proofs on reliable performance in terms of renewable bioenergy recovery such as methane (CH₄) production rate, CH₄ yield while removing volatile solid (VS) effectively. This study, therefore, aims to evaluate temperature-phased anaerobic sequencing batch reactor (TPASBR) system that is a promising approach for the sustainable treatment of organic fraction of municipal solid wastes (OFMSW). TPASBR system is compared with a conventional system, mesophilic two-stage anaerobic sequencing batch reactor system, which differs in operating temperature of 1st-stage. Results demonstrate that TPASBR system can obtain 44% VS removal from co-substrate of sewage sludge and food waste while producing 1.2 m³CH₄/m³_system/d (0.2 m³CH₄/kgVS_added) at organic loading rate of 6.1 gVS/L/d through the synergy of sequencing-batch operation, co-digestion, and temperature-phasing. Consequently, the rapid and balanced anaerobic metabolism at thermophilic stage makes TPASBR system to afford high organic loading rate showing superior performance on OFMSW stabilization.     

Treatment of landfill leachate using UASB-MBR-SHARON–Anammox configuration

Leachate treatment is a challenging issue due to its high pollutant loads. There are several studies on feasible treatment methods of leachate. In the scope of this study, high organic content of young leachate was eliminated using an upflow anaerobic sludge blanket (UASB) and a membrane bioreactor (MBR) in sequence and effluent of the system was given to single reactor for high activity ammonia removal over nitrite (SHARON) and anaerobic ammonia oxidation (Anammox) reactors to remove nitrogen content. All reactors were set up at lab scale in order to evaluate the usage of these processes in sequencing order for leachate treatment. COD and TKN removal efficiencies were over 90 % in the combined processes which were operated during the study. The biodegradable portion of organic matter was removed with an efficiency of 99 %. BOD₅ concentration decreased to 50 mg/L by UASB and MBR in sequence even the influent BOD₅ concentration was over 8,000 mg/L. Although high nitrogen concentrations were observed in raw leachate, successful removal of nitrogen was accomplished by consecutive operations of SHARON and Anammox reactors. The results of this study demonstrated that with an efficient pretreatment of leachate, the combination of SHARON–Anammox processes is an effective method for the treatment of high nitrogen content in leachate.     

Generating “Tide” in Pilot‐Scale Constructed Wetlands to Enhance Agricultural Wastewater Treatment

The operation of tidal flow was studied using a pilot‐scale system treating high strength piggery wastewater. Located on a farm in Staffordshire, UK, the system consisted of five wetland treatment stages vegetated with common reeds of Phragmites australis. Wastewater samples were collected from the inlet and outlet of each stage and analyzed for BOD₅, COD, NH₄‐N, NO₃‐N, NO₂‐N, SS, PO₄‐P and pH. Average hydraulic and organic loadings on the system were 0.12 m³/m² d and 240 g BOD/m² d, respectively, which is considerably higher than the typical loadings on conventional subsurface flow systems. On average, BOD₅ and COD were reduced by 82 % and 80 % from initial concentrations of 2000 mg/L and 2750 mg/L, respectively, across the whole system. The first‐order kinetics constant for BOD₅ removal (K_BOD in m/d) in this tidal flow system is approximately 2.5 times the rate constant obtainable in a typical horizontal flow system, demonstrating a more efficient removal of organic matter in tidal flow wetlands. The overall efficiency of the system was found to increase with time before stabilizing towards the end of a start‐up period. Straight‐line correlations were established between the loading and removal of BOD₅ and COD. Contributions by individual stages to the overall treatment were analyzed. SEM images of wetland media demonstrated the formation of biofilms and microbial activities inside the matrices of the wetland system, which accounted for the degradations of organic pollutants.     

Kraft mill anaerobic effluent color enhancement by a fixed-bed adsorption system

An anaerobic reactor and a fixed-bed adsorption sequential system (FBAS) were applied to remove color from kraft mill effluent. Under anaerobic conditions, Biological Oxygen Demand (BOD₅) removal was between 84 to 90% w/w, while Chemical Oxygen Demand (COD) removal ranged between 46 to 55% w/w. Total phenolic compounds were poorly removed (8 to 15% w/w) whereas the color was not removed by anaerobic digestion. For the FBAS system, three different columns were packed with natural and activated (calcinated and acidified) allophanic soil and fed with kraft mill anaerobic effluent. In activated soil columns, color and total phenolic compounds removal were around 95% w/w, whereas in the natural soil column the values were 87% w/w and 81% w/w, respectively.     

Treatment of pig manure liquid digestate in horizontal flow constructed wetlands: Effect of aeration

With the rapid development of scaled anaerobic digestion of pig manure, the generation of liquid anaerobic digestate exceeds the farmland loading capacity, causing serious environmental pollution. Three laboratory‐scale horizontal subsurface flow constructed wetlands (CWs; planted + aeration, planted, and unplanted) were set up to investigate the feasibility of liquid digestate treatment in wetlands. Treatment capacity in different wetlands was evaluated under different influent concentrations (chemical oxygen demand [COD], 5 days biochemical oxygen demand [BOD₅], and nitrogen forms). The effect of aeration and effluent recirculation on organic matter and total nitrogen removal was investigated. Results showed that integrating intermittent aeration in CWs significantly improved the oxygen condition (p < 0.01) in the wetland bed and promoted BOD₅ removal to 90% in aerated CWs as compared with <15% in the unaerated CWs. Meanwhile, COD removal between these three wetlands did not show any difference and varied from 52 to 72% under influent concentration of 200–820 mg/L because of the high content of hard‐degradable organic matter in the liquid digestate. Intermittent aeration resulted in high ammonium removal (>98%) although the influent loading varied from 65 to 350 mg/L. However, intermittent aeration caused nitrate accumulation of 300 mg/L and limited total nitrogen (TN) removal of 33%. To intensify the TN removal, we verified effluent recirculation to increase the removal efficiency of TN to 78%. These results not only show the potential application of CWs for treatment of high‐strength liquid anaerobic digested slurry, but also indicate the significance of intermittent aeration on the enhanced removal of organic matter and ammonium.     

Polishing low-biodegradable and saline industrial effluent in a full-scale horizontal subsurface flow constructed wetland: evaluation of bio-treatability and predictive power of kinetic models

Abstract

This study evaluates the bio-treatability performance and kinetic models of full-scale horizontal subsurface flow constructed wetland used for the tertiary treatment of composite industrial effluent characterized by high-salt content ranging from 5830 to 10,400 µS/cm and biochemical oxygen demand (BOD₅): chemical oxygen demand (COD) ratio below 0.2. The wetland vegetated with Phragmites australis was operated in a semi-arid climate under an average hydraulic loading rate of 63?mm/d. The results of a 4-year operation calculated based on the concentration of pollutants showed that the average removal efficiency of COD, BOD_5, and total suspended solids (TSS) were 17.5, 5.1, and 11.2%, respectively. The system reduced up to 6.5?±?0.7% of electrical conductivity presenting poor phyto-desalination potential without considering the contribution of evapotranspiration in water balance in contrast to satisfying performance for heavy metals reduction. The comparison of the kinetics of organic matter removal obtained by the first-order and Monod models paired with continuous stirred-tank reactor and plug flow regime showed that Monod-plug flow model provided the best fit with the constants of 2.01?g COD/m²·d and 0.3014?g BOD₅/m²·d with the best correlation coefficient of 0.610 and 0.968 between the predicted and measured concentrations, respectively. The low kinetic rates indicate that the process is capable of effluent polishing instead of purification due to the presence of organic compounds recalcitrant to biodegradation and a high level of salinity.     

Dyestuff wastewater treatment using chemical oxidation,physical adsorption and fixed bed biofilm process

Fenton’s oxidation and activated carbon adsorption were examined as pretreatment processes for dyestuff wastewater having high salinity, colour, and non-biodegradable organic concentrations. In this work, each wastewater stream produced by individual production processes was classified as streams R1, R2, and R3. The stream having a value of BOD₅/COD lower than 0.4 was pretreated by Fenton’s oxidation or activated carbon adsorption to increase the ratio of BOD₅/COD which indicates biodegradability. For Fenton’s oxidation with one stream having a value of BOD₅/COD lower than 0.4, the optimal reaction pH was 3.0 and the minimum dosing concentration (mg l⁻¹) of H₂O₂:FeSO₄·7H₂O was 700:3500. Stream R3, which consisted mainly of methanol was efficiently treated by activated carbon adsorption. The ratio of BOD₅/COD was also increased to 0.432 and 0.31 from 0.06 in Fenton’s oxidation and activated carbon adsorption, respectively. A biological treatment system using a fixed bed reactor was also investigated to enhance biological treatment efficiency at various hydraulic retention times, pretreatment conditions by Fenton’s reagent and salt concentrations by dyestuff wastewater. In addition, the efficiency of Fenton’s oxidation as a post-treatment system was also investigated to present a total treatment process of dyestuff wastewater. As the influent COD and salinity were increased, the effluent SS and COD were consequently increased. However, as the microorganisms became adapted to the changed influent condition, the treatment efficiency of the fixed bed reactor quickly recovered under the high COD and salinity since the microorganisms were well adapted to toxic influent conditions. A wastewater treatment process consisting of chemical oxidation, activated carbon adsorption, fixed bed biofilm process and Fenton’s oxidation as a post-treatment system can be useful to treat dyestuff wastewater having high salinity, colour, and non-biodegradable organic concentration.     

CONSTRUCTED WETLAND CONTROL OF BOD LEVELS IN AIRPORT RUNOFF

A surface water treatment system consisting of an aeration reservoir and pond (holding capacities 45,000 and 19,000 m³) and a network of 12 horizontal subsurface flow gravel-filled constructed wetland cells of different sizes (total surface area 2.08 ha) and planted with Phragmites australis, was commissioned at Heathrow Airport, London, United Kingdom, in the winter of 2002. Ongoing monitoring of the treatment system has shown significant reductions in the biochemical oxygen demand (BOD₅) throughout the system with levels decreasing by up to 76.7% across the constructed wetland cells following high anti- and de-icing fluid applications. However, continued exposure to BOD₅ concentrations exceeding the design target has resulted in anaerobic conditions in the wetland. The addition of nutrients to the treatment system has resulted in improved removal efficiency for elevated BOD₅ loadings in the aerated reservoir from 25.5% to 47.5%, The addition of different nutrient dosing regimes to complementary pilot-scale planted and unplanted vertical flow columns showed average but statistically insignificant BOD₅ removal percentage increases from 61.9 ± 21.1% to 70.8 ± 26.5%, respectively, in planted columns over a 7-day period. There is an overall improvement in the performance of the system, but operational reviews are continuing.     

Effect of agitation and aeration on the reduction of pollutant load of olive mill wastewater by the white-rot fungus Panus tigrinus

The white-rot fungus Panus tigrinus CBS 577.79 was cultivated both in mechanical (stirred tank, STR) and pneumatically (bubble column, BCB) agitated bioreactors and investigated for its ability to reduce the polluting load of olive-mill wastewater (OMW). Both aeration and agitation strongly influenced treatment efficiency. Best pollutants biodegradation performances were achieved in the bubble column bioreactor. Using this bioreactor, COD reduction, dephenolization and decoloration were 60.9, 97.2 and 75%, respectively. In contrast, lower depollution efficiency was generally observed in STR due to the possible occurrence of shear stress.     

Novel application of oxygen-transferring membranes to improve anaerobic wastewater treatment

Anaerobic biological wastewater treatment has numerous advantages over conventional aerobic processes; anaerobic biotechnologies, however, still have a reputation for low-quality effluents and operational instabilities. In this study, anaerobic bioreactors were augmented with an oxygen-transferring membrane to improve treatment performance. Two anaerobic bioreactors were fed a synthetic high-strength wastewater (chemical oxygen demand, or COD, of 11,000 mg l(-1)) and concurrently operated until biomass concentrations and effluent quality stabilized. Membrane aeration was then initiated in one of these bioreactors, leading to substantially improved COD removal efficiency (> 95%) compared to the unaerated control bioreactor (approximately 65%). The membrane-augmented anaerobic bioreactor required substantially less base addition to maintain circumneutral pH and exhibited 75% lower volatile fatty acid concentrations compared to the unaerated control bioreactor. The membrane-aerated bioreactor, however, failed to improve nitrogenous removal efficiency and produced 80% less biogas than the control bioreactor. A third membrane-augmented anaerobic bioreactor was operated to investigate the impact of start-up procedure on nitrogenous pollutant removal. In this bioreactor, excellent COD (>90%) and nitrogenous (>95%) pollutant removal efficiencies were observed at an intermediate COD concentration (5,500 mg l(-1)). Once the organic content of the influent wastewater was increased to full strength (COD = 11,000 mg l(-1)), however, nitrogenous pollutant removal stopped. This research demonstrates that partial aeration of anaerobic bioreactors using oxygen-transferring membranes is a novel approach to improve treatment performance. Additional research, however, is needed to optimize membrane surface area versus the organic loading rate to achieve the desired effluent quality.     

Seasonal and annual performance of a full-scale constructed wetland system for sewage treatment in China

A full-scale constructed wetlands system with a total area of 80 ha and treatment capability of 2.0 × 10⁴ m³ d⁻¹ was completed in October 1998 in Rongcheng, Shandong Province, China. To evaluate wastewater treatment effectiveness and seasonal performance of the system, water samples were collected and analyzed from January 1999 to December 2004. Comparison of mean inlet and outlet concentrations showed that the constructed wetland system could effectively reduce the output of SS (71.8 ± 8.4%), BOD₅ (70.4 ± 9.6%), COD (62.2 ± 10.1%), total coliform (99.7%) and fecal coliform (99.6%). However, the percent reduction of ammonia nitrogen was relatively low (40.6 ± 15.3%), and total phosphorus showed the least efficient reduction (29.6 ± 12.8%). BOD₅, COD, ammonia nitrogen, and total phosphorus removal efficiencies displayed seasonal variations. BOD₅ and COD removal was more efficient in spring and summer than in autumn and winter whereas ammonia nitrogen and total phosphorus removal was more efficient in summer and autumn than in spring and winter. Annual variation analysis shows that COD, BOD₅, and ammonia nitrogen reduction efficiencies increased from 1999 to 2004. In contrast, mean total phosphorus reduction efficiency did not change from 2001 to 2002 and began to decrease from 2003 onwards.     

Comparison of static,in-vessel composting of MSW with thermophilic anaerobic digestion and combinations of the two processes

The biological stabilisation of the organic fraction of municipal solid waste (OFMSW) into a form stable enough for land application can be achieved via aerobic or anaerobic treatments. To investigate the rates of degradation (e.g. via electron equivalents removed, or via carbon emitted) of aerobic and anaerobic treatment, OFMSW samples were exposed to computer controlled laboratory-scale aerobic (static in-vessel composting), and anaerobic (thermophilic anaerobic digestion with liquor recycle) treatment individually and in combination. A comparison of the degradation rates, based on electron flow revealed that provided a suitable inoculum was used, anaerobic digestion was the faster of the two waste conversion process. In addition to faster maximum substrate oxidation rates, anaerobic digestion (followed by post-treatment aerobic maturation), when compared to static composting alone, converted a larger fraction of the organics to gaseous end-products (CO₂ and CH₄), leading to improved end-product stability and maturity, as measured by compost self-heating and root elongation tests, respectively. While not comparable to windrow and other mixed, highly aerated compost systems, our results show that in the thermophilic, in-vessel treatment investigated here, the inclusion of a anaerobic phase, rather than using composting alone, improved hydrolysis rates as well as oxidation rates and product stability. The combination of the two methods, as used in the DiCOM^® process, was also tested allowing heat generation to thermophilic operating temperature, biogas recovery and a low odour stable end-product within 19 days of operation.     

Anaerobic treatment of kraft bleaching plant effluent

Anaerobic treatment of a kraft bleaching plant effluent was studied with focus on the removal of chlorinated organic compounds and biochemical O₂ demand (BOD). Experiments were carried out using a laboratory-scale anaerobic fixed-film process operated at different hydraulic retention times (HRTs). The process efficiently removed a variety of chloro-organic compounds when the HRT was 10 h or longer. However, a very long treatment time was required for significant removal of chlorofor; in fact, at the shortest HRT tested (6 h), there was a net production of chloroform. The overall removal of organically bound chlorine, measured as adsorbable organic halogens, was about 50%, and 60% removal of the extractable organic chlorine was achieved at an HRT of 15 h. About 70% of the BOD₇ and 20% of the chemical O₂ demand (COD) were removed. Up to 0.19 Nl of methane was produced per gram of COD removed by the treatment. When th HRT of the anaerobic process was shortened from 10 to 6 h, the methane production ceased. Correspondence to: Peijie Yu     

Evaluation of sludge reduction by an environmentally friendly chemical uncoupler in a pilot-scale anaerobic/anoxic/oxic process

An environmentally friendly chemical, tetrakis(hydroxymethyl)phosphonium sulfate (THPS), was used as a metabolic uncoupler to reduce sludge production in a pilot-scale anaerobic/anoxic/oxic process. The results show that the addition of THPS (1.08–1.86 mL/m³ influent) in the sludge return section could reduce waste activated sludge by about 22.5 %, and decrease the sludge yield by about 14.7 % at the end of a run. At the same time, the addition of THPS slightly lowered the removal of chemical oxygen demand (COD), soluble COD and NH₄ ⁺–N, and slightly improved removal of total nitrogen. The effects of THPS addition on two characteristics of activated sludge in oxic tank are discussed in detail and the results suggest that the settleability of sludge was reduced by addition of THPS, while the specific oxygen uptake rate was increased. Molecular biology analysis shows that the addition of THPS had little effect on the microbial communities of sludge.