Aerobic Activated Sludge Research Articles

Study on activated sludge composition and concentration setting for increasing COD efficiency in dairy industry wastewater

The dairy industry’s wastewater is the pollution problems that must be concerned. Since dairy wastewater tends to be easily biodegradable, the commonly wastewater treatment technology is biological treatment. The efficiency of reducing COD in the aeration tank of PT. AN was about 39.54% compared to the theoretical that can be achieved until 90%. Therefore, this research objective was to improve the efficiency of COD reduction in the aerobic-activated sludge process of PT. AN. The research was done by laboratory experimental method with variations of the concentration and type of the activated sludge applied, also variations in Bacillus cereus bacteria addition. The performance was measured by the COD reduction efficiency after 9-hour aeration and 3-hour sedimentation. The result showed that by increasing 100% of the activated sludge concentration, the process could increase the COD reduction from 20.3% to 49.8%. The 50:50 combination of existing activated sludge and other activate sludge taken from non-dairy industry’s WWTP got worse result, with the COD reduction from 20.3% to 15.9 %. The better result was shown by Bacillus cereus bacteria addition, the COD reduction can achieve 67.0% with 4.7 % bacteria addition and 97.0% COD reduction can be achieved with 9% bacteria addition.

Co-Treatment of Winery and Domestic Wastewaters in Municipal Wastewater Treatment Plants: Analysis of Biodegradation Kinetics and Process Performance Impacts

Winery wastewater (WWW) handling strategies often include co-treatment at municipal wastewater treatment plants (WWTPs). Despite this, definitive information regarding oxidation kinetics and process and performance impacts due to co-treatment is lacking. A combined Michaelis–Menten–University of Cape Town kinetic model has been found to best describe the pH-inhibited aerobic biological oxidation of WWW by heterotrophs in activated sludge from four municipal WWTPs. The specific rate of substrate consumption was highest in biomass that had been exposed to WWW (57.3 mg COD/g MLVSS·h) compared to biomass that had not (20.7 mg COD/g MLVSS·h). Bench-scale aerobic co-treatment trials confirm that sorption is a key removal mechanism, with up to 98% chemical oxygen demand and 97% total organic carbon removal after 6 h of reaction time. The WWW solids are quickly incorporated into the biological floc and may improve settleability at loading rates above 75 mg WWW suspended solids/L bioreactor volume at the expense of significantly increasing the observed yield. The aerobic-activated sludge system at municipal WWTPs can effectively co-treat WWW, provided the organic loading rates are limited and the WWTP is designed to accommodate the seasonal loadings of winery wastewater. The identified mitigation measures can be used by co-treating facilities to optimize the co-treatment performance of WWW along with domestic wastewater.

Occurrence and the potential ecological risk of veterinary antimicrobials in swine farm wastewaters in Japan: Seasonal changes, relation to purchased quantity and after termination of oxytetracycline usage

This study provides the first comprehensive investigation of the residual concentrations of eight classes of antimicrobial agents (AMs, 20 compounds) in 13 swine wastewater treatment facilities in Japan. These facilities implemented the aerobic activated sludge (AS) or its alternative methods. The maximum concentrations before treatment were found at the level of 7100, 6900, 6000, 3600, 3400, and 1400 µg/L for tilmicosin, oxytetracycline (OTC), chlortetracycline, lincomycin , sulfamethoxazole, and trimethoprim, respectively. The highest detection rate (96.3%) in influents was noted for the morantel, which was a feed additive. The seasonal difference in residual concentration was much greater for tetracyclines (TCs) and macrolides (MLs) when their residual concentrations were high, especially in the cold season. There was a positive correlation between the purchased quantity of TCs and fluoroquinolones (FQs) and their residue levels detected in the effluents (p < 0.01). The estimated removal rate of AMs was greater than 80%. In contrast, on a few occasions, it was diminished due to failing operating conditions, such as water temperature and AS rate in the aeration tank. The estimated ecological risks of AMs in effluents based on risk quotients (RQs) considered to enhance the selection pressure for drug resistance (RQs-AMR) were high for TCs and FQs, whereas ecotoxicological effects (RQs-ENV) to aquatic organisms were higher for sulfonamides and MLs. When OTC usage ceased, its concentration in wastewater decreased rapidly; however, it remained longer period in the effluents, probably due to OTC desorption from the AS. The concentrations (and respective RQs) of TCs were decreased by >99.8% and >92% in the influents and effluents, respectively. This data suggested that it is essential to reduce the amount used and introduce more efficient methods and operating conditions to constantly remove AMs during the treatment to reduce the risk of AM discharge from swine farms.

Biodecolorization and Ecotoxicity Abatement of Disperse Dye-Production Wastewater Treatment with Pycnoporus Laccase.

The biological treatment efficiency of dye wastewater using activated sludge (AS) is largely limited to the chromaticity and ecotoxicity of dyestuff. To alleviate this limitation, eleven industrial-grade disperse dyes were obtained from a fiber-dyeing factory, and for the first time, we studied the decolorization and detoxification effects of using the Pycnoporus laccase enzyme. Efficient decolorization was achieved with the following conditions: dye concentration 50 mg/L, 1-hydroxybenzotriazole (HBT) 0.15 mM, temperature 65 °C, pH 4, and laccase 0.33 U/mL. The decolorization rate of disperse dyes, ranging from 51 to 96% in this investigation, was highly dependent on the dye type, concentration, laccase loading, and HBT. The ecotoxicity of dyes was evaluated by studying the germination/growth of wheat seed as well as the respiratory rate of aerobic AS. Laccase treatment mitigated the phytotoxicity of dyes because of the higher wheat germination (e.g., increase of 38% for Black ECT 200%) and growth rate (e.g., increase of 91% for Blue 2BLN 200%). The reduced ecotoxicity of decolorized dye solution towards microorganisms was also confirmed by the finding that the oxygen uptake by aerobic AS was increased relative to that of the untreated samples (e.g., increase of 14 folds for Blue HGL 200%). In addition, the chemical oxygen demand (COD) of decolorized dye solution was slightly lower than that without decolorization during the respiratory test. The experimental results suggest that enzymatic decolorization and detoxification can be potentially used as a pretreatment method for disperse dye wastewater followed by AS treatment.

Advances in biodegradation of sulfonamides antibiotics in aerobic activated sludge system

Sulfonamides (SAs) are a kind of antibiotics widely used in medical treatment and livestock breeding. However, they have poor degradability in human and animal intestines, and will enter the sewage treatment system through the discharge of feces and urine. The aerobic activated sludge (AAS) in wastewater treatment plant was found to be able to effectively transform SAs. This article summarizes the advances in biodegradation of SAs in aerobic activated sludge system, which includes the biodegradation mechanisms, the main biodegradation pathways, and the environmental factors affecting the degradation efficiency. Challenges encountered in the current research were discussed, with the aim to provide scientific basis for optimizing the biodegradation of SAs in wastewater treatment process.

Comprehensive insights into core microbial assemblages in activated sludge exposed to textile-dyeing wastewater stress

Microorganisms in activated sludge are widely recognized for their roles in wastewater treatment. However, previous studies were mainly concerned with the diversity and driving factors of microbial communities within domestic wastewater treatment, and those of domestic wastewater treatment systems mixed with industrial wastewater are poorly understood. In this research, three different full-scale aerobic activated sludge (AS) wastewater treatment systems fed with municipal, textile-dyeing, and mixed wastewater, respectively, were monitored over the operation course of three months. 16S rRNA amplicon sequencing analysis revealed that the microbial communities in textile-dyeing wastewater activated sludge (AS) exhibited significantly lower richness and diversity (p < 0.01, Adonis) compared to those fed with municipal wastewater. In contrast, textile-dyeing derived AS selectively enriched microbial taxa with aromatic degradation and denitrification potentials. Further, FARPROTAX and metabolomics indicated the inhibition of 72.5% metabolic functions (p < 0.01) in AS from the system fed with textile-dyeing wastewater, including the pathways of pentose phosphate metabolism, purine metabolism, and glycerophospholipid metabolism. Overall, this study corroborates textile-dyeing wastewater is a novel microbial niche and could suppress sludge performance by inhibiting microbial activity and metabolism, raising concerns on AS-based systems for industrial wastewater treatment.

Life-Cycle Assessment of the Wastewater Treatment Technologies in Indonesia’s Fish-Processing Industry

In this paper, a comprehensive life-cycle assessment (LCA) is carried out in order to evaluate the multiple environmental-health impacts of the biological wastewater treatment of the fish-processing industry throughout its life cycle. To this aim, the life-cycle impact assessment method based on endpoint modeling (LIME) was considered as the main LCA model. The proposed methodology is based on an endpoint modeling framework that uses the conjoint analysis to calculate damage factors for human health, social assets, biodiversity, and primary production, based on Indonesia’s local data inventory. A quantitative microbial risk assessment (QMRA) is integrated with the LIME modeling framework to evaluate the damage on human health caused by five major biological treatment technologies, including chemical-enhanced primary clarification (CEPC), aerobic-activated sludge (AS), up-flow anaerobic sludge blanket (UASB), ultrafiltration (UF) and reverse osmosis (RO) in this industry. Finally, a life-cycle costing (LCC) is carried out, considering all the costs incurred during the lifetime. The LCA results revealed that air pollution and gaseous emissions from electricity consumption have the most significant environmental impacts in all scenarios and all categories. The combined utilization of the UF and RO technologies in the secondary and tertiary treatment processes reduces the health damage caused by microbial diseases, which contributes significantly to reducing overall environmental damage.

Highly effective treatment of petrochemical wastewater by a super-sized industrial scale plant with expanded granular sludge bed bioreactor and aerobic activated sludge

One industrial scale plant has been constructed for annual treatment of 657,000 m3 real petrochemical wastewater of 4649 ± 651 mg/l COD and more than 50 mg/l petrochemicals. The plant system is divided into four parts, and the treatment process mainly functions in a 2200 m3 anaerobic expanded granular sludge bed (EGSB) bioreactor and a 10,000 m3 aerobic activated sludge (AS) bioreactor with the hydraulic retention time (HRT) of 62.8 h and 133.3 h, respectively. The plant has been successfully operated for more than 450 days, and the overall COD and petrochemical removal efficiencies of the plant are 85.6 ± 2.5% and 81.5 ± 4.8%, respectively. The removal efficiency of the aerobic AS bioreactor was higher than that of the anaerobic EGSB bioreactor, and most COD and petrochemicals were removed in the aerobic AS bioreactor. Further microbial diversity analysis revealed that the dominant microbes in the EGSB and AS bioreactors were assigned to Proteobacteria and Firmicutes and 4 dominant OTUs related with COD or petrochemicals removal were enriched in the bioreactors, showing that the microbial communities had been adapted to the petrochemical wastewater treatment. Based on the results, the newly built industrial plant exhibited good performance in petrochemical wastewater treatment and enriched microbes towards petrochemical wastewater treatment during operation. This strategy also has potential applications for other industrial wastewater treatment in the future.

Insights into the methanogenic degradation of N, N-dimethylformamide: The functional microorganisms and their ecological relationships

The methanogenic degradation of N, N-dimethylformamide (DMF) was investigated using anaerobic digested sludge (ADS), aerobic activated sludge (AAS) and co-cultured sludge (CCS), respectively. Both the metabolic pathway and the corresponding microorganisms which function in the methanogenic degradation of DMF were elucidated. DMF was unable to be degraded anaerobically by ADS due to the lack of DMF-hydrolyzing bacteria. DMF can be effectively degraded by AAS, however, no methane was recovered under the aerobic condition. The co-culture of DMF-hydrolyzing bacteria and methanogens in the CCS allowed for both hydrolysis of DMF and methane production to proceed successfully under the anaerobic condition, realizing the complete conversion from DMF to methane. However, a niche overlap due to the competition for the intermediates lowered the abundance of DMF-hydrolyzing bacteria. The introduction of nitrate, timely replenishment of AAS, micro-aeration and co-digestion were likely to maintain a high abundance of DMF-hydrolyzing bacteria to ensure an effective hydrolysis.

Hydrogen Production Using “Direct-Starting” Biocathode Microbial Electrolysis Cell and the Analysis of Microbial Communities

In this study, a “direct-starting” procedure was used to activate a single-chamber biocathode microbial electrolysis cell (MEC) and the development of a biocathode was studied through output current curves and cyclic voltammograms. It only took 163 h for a successful start-up, and a current density of 14.75 A/m2 was obtained. In the formal hydrogen-production stage, it was found that the biocathode MEC was comparable with the Pt/C cathode MEC in terms of current density and energy efficiency, and the hydrogen recovery, cathodic hydrogen recovery, and hydrogen production rate of the biocathode MEC were 71.22% ± 8.98%, 79.42% ± 5.94%, and 0.428 ± 0.054 m3 H2/m3 · days, respectively, which were slightly higher than those obtained with the Pt/C cathode MEC. Besides, under the effect of applied voltage, the microbial populations in the anodophilic biofilm of MEC (MECan) and the cathodophilic biofilm of MEC (MECca) were less diverse than those of the original aerobic activated sludge (AAS) and the anodophilic biofilm of MEC (MECan). Furthermore, the microbial community structures evidently differed between MECan/MECca and AAS/MFC.

Treatment of actual slaughterhouse wastewater by combined anaerobic–aerobic processes for biogas generation and removal of organics and nutrients: An optimization study towards a cleaner production in the meat processing industry

Environmental protection initiatives and the increasing market demands for green practices are driving the meat processing industry to consider sustainable methods for wastewater treatment since slaughterhouse wastewater (SWW) is seen as detrimental worldwide. Thus, on-site treatment is the preferred option to treat the slaughterhouse effluents for water reuse and potential energy recovery due to the conversion of organics into biogas. The treatment of an actual SWW is studied in a combined biological system, including aerobic and anaerobic processes. An anaerobic baffled reactor (ABR) followed by an aerobic activated sludge (AS) reactor are used in continuous mode at laboratory scale. Response surface methodology (RSM) is used for the process optimization to maximize biogas yield and to remove the total organic carbon (TOC) and total nitrogen (TN) while minimizing the total suspended solids (TSS) residuals. The effects of the flow rate, the pH, the influent TOC concentration, and their interactions on the overall treatment efficiency as well as the biogas yield are studied. Maximum TOC and TN removals of 85.03 and 72.10%, minimum TSS residual of 19.54 mg/L, and maximum biogas yield of 116.56 mL/min are found at the optimum operating conditions of the influent TOC concentration of 343 mg/L, the feed flow rate of 63 mL/min, and the pH of 6.84. The agreement between model predictions and experimental values indicates that the proposed model could describe the performance of combined anaerobic–aerobic systems for SWW treatment and the reduction of operating costs via biogas production while providing high-quality treated effluent for water reuse.

Combined photocatalysis and membrane bioreactor for the treatment of feedwater containing thin film transistor-liquid crystal display discharge

The nitrogen content of waste water generated by the thin film transistor-liquid crystal display (TFT-LCD) industry is not satisfactorily removed through the conventional aerobic-activated sludge process. In this study, the performance of three reactors – suspended type TiO2 membrane photoreactor (MPR), anoxic/oxic membrane bioreactor (AOMBR), and their combination (MPR-AOMBR) – was evaluated using feedwater containing TFT-LCD discharge. The parameters that maximized monoethanolamine (MEA) removal in the MPR were continuous ultraviolet (UV) irradiation and pH 11. Among the tested loadings, 0.1 g/l of TiO2 promoted MEA removal but degradation rate may further increase with photocatalyst concentration. The nitrified sludge recycle ratio R of the AOMBR was adjusted to 1.5 to minimize the amount of nitrate in the effluent. The AOMBR greatly decreased chemical oxygen demand and MEA, but removed only 32.7% of tetramethyl ammonium hydroxide (TMAH). The MPR was configured as the pre-treatment unit for AOMBR, and the combined MPR-AOMBR has improved TMAH removal by 80.1%. The MPR bolstered performance by decomposing slowly biodegradable compounds, and had no negative effects on denitrification and carbon removal.

Performance appraisal of the A2/O process in domestic wastewater treatment replacing the anaerobic unit with UASB

Feasibility of a combined system consisting of an anaerobic up-flow anaerobic sludge blanket (UASB) followed by anoxic unit then aerobic activated sludge (AS) was investigated.The system was fed with normal domestic wastewater, then medium loading wastewater using activated sludge from El Berka WWTP, then high strength sewage having a chemical oxygen demand (COD) of 2635mg COD/L. The organic loading rate (OLR) was increased gradually from 0.5 to 4.43kg COD/m3/day. The HRT was changed for each loading from 10.5 to 15h. The internal recirculation (IR) was tested at 100%, 200% and 300% for each loading run. The return activated sludge was adjusted to maintain a mixed liquor suspended solids of greater than 2500ppm.At steady state conditions, the UASB reactor achieved removal efficiency up to 79.13% of the total COD. The combined system performed an excellent organic removal pushing the overall removal efficiency of the total COD, TN and TP to 95.87%, 84.95% and 87.59%, respectively.When the OLR increased to 4.43kg COD/m3/day, the effluent quality of the UASB deteriorated reaching a percent of 48.20 for COD removal efficiency dropped to 62.90%, 29.90% and 46.90% respectively.The optimum operational conditions for the system on different organic loadings were HRT=15h and the IR=200%.

Acclimation of aerobic-activated sludge degrading benzene derivatives and co-metabolic degradation activities of trichloroethylene by benzene derivative-grown aerobic sludge

The acclimation of aerobic-activated sludge for degradation of benzene derivatives was investigated in batch experiments. Phenol, benzoic acid, toluene, aniline and chlorobenzene were concurrently added to five different bioreactors which contained the aerobic-activated sludge. After the acclimation process ended, the acclimated phenol-, benzoic acid-, toluene-, aniline- and chlorobenzene-grown aerobic-activated sludge were used to explore the co-metabolic degradation activities of trichloroethylene (TCE). Monod equation was employed to simulate the kinetics of co-metabolic degradation of TCE by benzene derivative-grown sludge. At the end of experiments, the mixed microbial communities grown under different conditions were identified. The results showed that the acclimation periods of microorganisms for different benzene derivatives varied. The maximum degradation rates of TCE for phenol-, benzoic acid-, toluene-, aniline- and chlorobenzene-grown aerobic sludge were 0.020, 0.017, 0.016, 0.0089 and 0.0047 mg g SS−1 h−1, respectively. The kinetic of TCE degradation in the absence of benzene derivative followed Monod equation well. Also, eight phyla were observed in the acclimated benzene derivative-grown aerobic sludge. Each of benzene derivative-grown aerobic sludge had different microbial community composition. This study can hopefully add new knowledge to the area of TCE co-metabolic by mixed microbial communities, and further the understanding on the function and applicability of aerobic-activated sludge.

Combination of sonophotolysis and aerobic activated sludge processes for treatment of synthetic pharmaceutical wastewater

The performance and effectiveness of sonophotolytic process, aerobic activated sludge (AS) process, and their combination in reduction of total organic carbon (TOC), chemical oxygen demand (COD), and biological oxygen demand (BOD) from a synthetic pharmaceutical wastewater (SPWW) are evaluated. Batch mode experiments are performed to obtain optimal experimental operating conditions of the sonophotolytic process. An ultrasonic power of 140 W, initial pH solution of 2, and air flow rate of 3 L min−1 are found to be optimal operating conditions. The initial optimum molar ratio of H2O2/TOC was found to be 13.77 for the sonophotolytic process operated in batch mode. In continuous mode, a 90% TOC reduction was obtained in the sonophotolytic process after 180 min retention time, whereas only 67% in an aerobic AS process for retention time of 48 h. However, combined sonophotolytic and aerobic AS processes improved the biodegradability of the SPWW with 98% TOC and 99% COD removal while reducing the retention time in sonophotoreactor and aerobic AS bioreactor to 120 min and 24 h, respectively. Besides, the consumption of H2O2 was reduced significantly in the combined processes.

Determination of sorption properties of micropollutants: What is the most suitable activated sludge inhibition technique to preserve the biomass structure?

Apart from providing a total activated sludge (AS) inhibition, an efficient AS inhibition technique must preserve the biomass structure in order to maintain the real sorption phenomenon. Many inhibition techniques with different modes of action were used in previous studies for AS inhibition. But, the effectiveness of AS deactivation and the adverse effects on the biomass structure were rarely related. In this paper, five common AS inhibition techniques were evaluated: thermal, three chemical and gas purging techniques. The lowest chemical effective concentrations were determined in order to limit the negative impact on the AS structure. 100mgHg2SO4gTSS−1 and 30mgHgCl2gTSS−1 within 2h of reaction were enough to provide a complete AS inhibition. However, after 20h of reaction a full AS inhibition has never been achieved with sodium azide at 200mgNaN3gTSS−1, even by increasing NaN3 concentration.The analysis of the AS apparent viscosity, the median size D50 of the flocs and the supernatant turbidity showed that the thermal technique destructured the AS completely. A significant AS deflocculation is induced by the three chemical reagents depending on the mode of action and the concentration used. Thermal and chemical inactivations are therefore not suitable to determine sorption properties. The only technique which kept the initial AS structure unchanged has several drawbacks since (i) a reaction might occur between the gas and the analyte of interest, and (ii) anaerobic activated sludge are not inhibited by this technique. Therefore, the establishment of anaerobic conditions without gas injection is recommended for implementing sorption experiments on aerobic AS.

Combined anaerobic-aerobic and UV/H2O2 processes for the treatment of synthetic slaughterhouse wastewater

The biological treatment of a synthetic slaughterhouse wastewater (SSWW) is studied using an anaerobic baffled bioreactor (ABR) and an aerobic activated sludge (AS) at a laboratory scale in continuous mode. The total organic carbon (TOC) loading rate, the total nitrogen (TN) loading rate, and the flow rate are 0.03–1.01 g/(L.day), 0.01–0.19 g/(L.day), and 2.93–11.70 mL/min, respectively. The results reveal that combined anaerobic-aerobic processes had higher efficiency to treat SSWW than a single process. Up to 96.36% TOC, 80.53% TN, and 99.38% 5-day carbonaceous biochemical oxygen demand (CBOD5) removal from an influent concentration of 1,009 mgTOC/L, 420 mgTN/L, and 640 mgCBOD5/L at the hydraulic retention time (HRT) of 6.24 days and a flow rate of 3.75 mL/min are achieved. The UV/H2O2 process is studied to treat a secondary effluent of SSWW with TOC loadings of 65–350 mg/L. Up to 75.22% TOC and 84.38% CBOD5 removal are obtained at the HRT of 3 h with H2O2 concentration of 900 mg/L. Optimum molar ratios of 13.87 mgH2O2/mgTOCin and 4.62 mgH2O2/mgTOCin.h are also obtained. Combined anaerobic-aerobic and UV/H2O2 processes enhanced the biodegradability of the TOC, TN, and CBOD5 present in the SSWW. Up to 99.98% TOC, 82.84% TN, and 99.69% CBOD5 overall removals are obtained for an influent concentration of 1,005 mgTOC/L, 200 mgTN/L, and 640 mgCBOD5/L at the HRT of 4 days and a flow-rate of 5.90 mL/min.

Anaerobic–aerobic sequencing bioreactors improve energy efficiency for treatment of personal care product industry wastes

Personal care product (PCP) industry liquid wastes contain shampoo residues, which are usually treated by aerobic activated sludge (AS). Unfortunately, AS is expensive for PCP wastes because of high aeration and energy demands, whereas potentially energy-positive anaerobic designs cannot meet effluent targets. Therefore, combined anaerobic-aerobic systems may be the best solution. Seven treatment systems were assessed in terms of energy and treatment performance for shampoo wastes, including one aerobic, three anaerobic (HUASB, AHR and AnCSTR) and three anaerobic-aerobic reactor designs. COD removals were highest in the HUASB-aerobic (87.9 ± 0.4%) and AHR-aerobic (86.8±0.5%) systems, which used 69.2% and 62.5% less energy than aerobic AS. However, actual methane production rates were low relative to theoretical in the UASB and AHR units (∼10% methane/COD removed) compared with the AnCSTR unit (∼70%). Anaerobic-aerobic sequence reactors show promise for treating shampoo wastes, but optimal designs depend upon whether methane production or COD removal is most important to operations.

Treatment of high-strength synthetic sewage in a laboratory-scale upflow anaerobic sludge bed (UASB) with aerobic activated sludge (AS) post-treatment

Performance of a combined system up-flow anaerobic sludge blanket (UASB) followed by aerobic treatment activated sludge (AS) for removal of carbonaceous and nitrogenous contaminants at an average temperature of 25°C was investigated. The combined system was fed with high strength synthetic sewage having chemical oxygen demand (COD) of 2500 mg L−1. The organic loading rate (OLR) of the UASB reactor was increased gradually from 1.1 to 3.8 gCOD Lr −1 d−1. At steady state condition, the UASB reactor achieved removal efficiency up to 83.5% of total COD (CODtot), 74.0% of volatile fatty acid (VFA) and 94.0% of protein. The combined system performed an excellent organic removal pushing the overall removal efficiency of CODtot, VFA and protein to 91.0%, 99.9% and 98.2%, respectively. When the OLR of the UASB increased to 4.4 g COD Lr −1 d−1, the UASB was overloaded and; thus, its effluent quality deteriorated. In respect to nitrogen removal, both partial nitrification and complete nitrification took place in aerobic post-treatment. When the dissolved oxygen (DO) concentration was >2.0 mg L−1, complete nitrification (period B) occurred with an average nitrification efficiency of 96.2%. The partial nitrification occurred due to high OLR to AS during the overloading event (period A) and when DO concentration was <2.0 mg L−1 (period C). The maximum accumulated nitrite concentration in periods A, B and C were 90.0, 0.9 and 75.8 mg NO− 2 -N L−1, respectively. The nitrogen balance results of periods A and C indicated that there was a discrepancy between the amount of ammonium nitrogen removed and the amount of oxidized nitrogen formed. This suggests the occurrence of simultaneous nitrification/denitrification (SND) in aerobic post-treatment.

Low-energy treatment of colourant wastes using sponge biofilters for the personal care product industry

Four trickling biofilter designs were assessed as low-energy alternatives to aerobic activated sludge (AS) for the treatment of personal care product industry wastes. The designs included partially submerged packed-media and sponge reactors with and without active aeration. Partial submergence was used to reduce active aeration needs. Simulated colourant wastes (up to COD=12,480mg/L, TN=128mg/L) were treated for 201days, including wastes with elevated oxidant levels. COD and TN removal efficiencies were always >79% and >30% (even without aeration). However, aerated sponge reactors consistently had the highest removal efficiencies, especially for TN (∼60%), and were most tolerant of elevated oxidants. This study shows sponge biofilters have great potential for treating colourant wastes because they achieve high treatment efficiencies and reduce energy use by >40% relative to AS systems.