Substrate removal kinetics in an upflow anaerobic sludge blanket reactor decolorising simulated textile wastewater

Performance enhancement of up-flow anaerobic sludge blanket reactor for psychrophilic temperature during the dry season: Kality wastewater treatment plant

The main purpose of wastewater treatment plant (WWTP) is to reduce organic and inorganic pollutants to meet standards. But WWTPs employing up flow anaerobic sludge blanket (UASB) reactors under psychrophilic temperature are currently removing about 55% chemical oxygen demand (COD) and 70% total dissolved solids (TSS). The research was done to increase the treatment efficiencies of UASB reactor working under psychrophilic conditions through optimization of operational parameters like temperature, organic loading rate (OLR), pH and hydraulic retention time (HRT). Experimentation was carried out in a 0.0486 m3 square-shaped pilot-scale UASB reactor. Experimental design response surface method (RSM) for performance enhancement and optimization of UASB reactor operational parameters through five levels of central composite design (CCD) was used. The optimized operational parameters obtained from CCD-RSM were as follows: temperature of 21.58 °C, OLR of 2.99 kg COD/m3.d, HRT of 4.37hrs and pH of 6.3. Using optimized parameters, tests yielded efficiencies of 92.70%, 99.06%, and 94.50% for COD, TSS, and volatile suspended solid (VSS) respectively. The outlet concentrations of alkalinity, and volatile fatty acids (VFA), were found to be lower than the inlet concentrations. The alkalinity in the system accepts the hydrogen ion released by acids and the system is taken over by methanogensis to maintain the pH. The outlet concentration of sulfate ion was found to be increasing due to inhabitation of sulfur-reducing bacteria by an anaerobic condition of VFA and alkalinity at a pH less than 7.8.This process favors the production of CH4 than H2S gas. In general, there was a high likelihood of improving the performance of UASB reactor operating at psychrophilic temperature by optimizing operational parameters.

A kinetic study on the nitrification process in the upflow submerged biofilter reactor

In extent of this study, ammonium removal from wastewater through biological nitrification process was performed in upflow biofilm reactors. The effects of hydraulic retention time (HRT) and nitrogen loading rate (NLR) on the nitrification process were investigated. For the nitrification process, the optimum HRT and NLR were determined to be 80 hr and 0.044 kg/m³.day, respectively. It is observed that the efficiency increased from 53% to 96% along with the increase in HRT from 22 hr to 80 hr and the decrease in NLR from 0.165 kg/m³.day to 0.044 kg/m³.day.The substrate consumption kinetics were studied in the attached growth reactor, and the Monod kinetic model, first-order kinetic model, modified Stover-Kincannon and Grau second-order kinetic models were examined. For the substrate consumption kinetic study, experimental studies were performed at 125, 150, 175, 200, 225 mg NH₄-N/L substrate concentrations and 62 hr at HRT during the nitrification process. As a result of the considering kinetic studies, it was determined that the kinetic study was suitable for the modified Stover-Kincannon kinetic model that had the highest coefficient of regression by 0.997 and when the effluent NH₄-N concentrations and NH₄-N removal efficiencies calculated using kinetic models were examined, it was observed that the results closest to the experimental results (4.5, 10.1, 19.7, 26.2 and 42.3 mg NH₄-N/L) were obtained through the modified Stover-Kincannon model (4.16, 10.71, 18.92, 28.12 and 39.51 mg NH₄-N/L).

Performance evaluation and kinetics modeling of a hybrid UASB reactor treating bovine slaughterhouse wastewater

This work aimed to analyze the performance of a hybrid upflow anaerobic sludge blanket (HUASB) reactor packed with natural zeolite for slaughterhouse wastewater treatment through kinetics modeling. Wastewater samples from a municipal bovine slaughterhouse were sieved through a 1-mm mesh screen and thermally pretreated in an autoclave. Then, biological treatment was carried out in a HUASB reactor packed with a zeolite filter at the top. Slaughterhouse wastewater was diluted with municipal wastewater during the start-up period to achieve a low organic loading rate (OLR) (3.4 kg chemical oxygen demand (COD)/m3/day); afterward, it gradually increased until dilution was eliminated, reaching 14.4 kg COD/m3/day. At this OLR, the maximum percentage removals of total COD, soluble COD, total solid, and volatile solid (67.7%, 68.3%, 55.2%, and 72.1%, respectively) were found. Moreover, the zeolite filter enabled NH4+-N and PO43--P removal, with the highest values (32.8% and 35%, respectively) at 9.8 kg COD/m3/day. Thus, the natural zeolite filter improved the reactor's performance. Among all equations analyzed, the modified Stover-Kincannon equation correctly fitted the results and provided the best prediction of the HUASB reactor's performance.

Kinetic evaluation of sonicated food waste in continuously stirred tank reactor

This work aimed to evaluate the process performance and stability of the anaerobic digestion of sonicated food waste (SFW) by determining the kinetic parameters using Monod, Contois, Modified Stover-Kincannon, and Grau second-order multicomponent substrate removal kinetic models. The anaerobic digestion was conducted on the sonicated food waste (SFW) in a 13 L continuously stirred tank reactor (CSTR) with a stepwise organic loading rate (OLR) ranging from 1.5 to 3.5 gCOD/L.day. The experimental works were carried out in two stages (start-up then followed by semi-continuous). The ultrasonic pretreatment was performed by sonicating the food waste slurry for 10 minutes at a 20 kHz frequency and specific energy input of 25,997 kJ/kg TS. The process performance, as well as acceptable stability in the SFW digester, provided satisfactory predictions with Monod, Modified Stover-Kincannon, Grau second-order multicomponent substrate removal, and Contois kinetic models. A significant relationship was seen between the predicted and experimental data with correlation coefficients (R²) ranging from 0.893 to 0.996. In this study, the Monod model with R² = 0.996 indicates the most suitable model for understanding the kinetic parameters of the anaerobic system in the CSTR which digests the sonicated food waste (SFW) slurry.

The Control Strategy and Kinetics of VFAs Production in an ASBR Reactor Treating Low-Strength Mariculture Wastewater

As an environment-friendly wastewater treatment process, the anaerobic fermentation process has been widely used for the pretreatment of high-strength wastewater. However, it is rarely applied to treat low-strength wastewater due to low methane recovery. In this study, anaerobic fermentation treating low-strength mariculture wastewater was studied in an anaerobic sequencing batch reactor (ASBR) with a COD removal rate of 75%. Anaerobic fermentation was successfully controlled at the acidification stage by increasing COD loading. As the greenhouse gas emission decreased, the residual organics were enough for biological nutrients’ removal. Fluorescence in situ hybridization results showed that the dominant bacteria in the ASBR were acidogenic bacteria and methanogens, accounting for 39.7% and 46.5% of the total bacteria, respectively. Through the calculation processing of the experimental data, the order of the anaerobic fermentation reaction was a second-order reaction. The kinetic parameters of low-strength organic wastewater treatment were determined by using the Grau second-order substrate removal model, Stover–Kincannon model, Monod model and Haldane model. The maximum rate removal constant U_max, sludge yield coefficient Y and inhibition constant K_i were 1.157 g/(L·d), 0.153 mgVSS/mgCOD and 670 mg/L, respectively. It provided data support for the practical application of the anaerobic fermentation treating low-strength wastewater.

Performance evaluation and kinetic modeling of an upflow anaerobic sludge blanket septic tank for domestic wastewater treatment

This work evaluated the UASB-septic tank performance using different kinetic models that correlated process efficiency and methane production with hydraulic and organic loading rates through experiments with five different HRT (48 h, 36 h, 24 h, 18 h, and 12 h) using synthetic domestic wastewater. The modified Stover-Kincannon model provided the best fitting to calculate kinetics constants, with an R2 above 98% for linear regression, and predicted the effluent COD more accurately than the other models. Methane yield was 0.3294 L CH4/g COD removed, being closer to the theoretical value, and the Van der Meer and Heertjes model had the highest R2 for methane production. Organic matter and solids removal were 45% for TS, 70% and 68% for total and soluble COD, and 85% for TSS. Pollutant removal markedly decreased when the reactor operated HRT below 24 h; thus, it is recommended to operate the UASB-septic tank at this HRT.

Biodegradation of acid red 3BN dye in sequential batch reactor: parameters and kinetics studies

Textile and dye industries generate wastewater which is considered as highly polluted and carcinogenic. Due to this, treatment of wastewater is required earlier to discharge or recycle. In the present studies, treatment of dye bearing water (DBW) has been explored. The treatment was performed using activated sludge (mixed culture) for aerobic process in sequential batch reactor (SBR). The fill volume (V F) and fill time (t F) variation in the treatment of DBW was taken place. The initial value of dye concentration, chemical oxygen demand (COD), sludge, and hydraulic retention time (HRT) were found to play important role in the treatment. At optimum condition (HRT = 2.5 d), the 86.84% COD reduction of 190 mg/L COD, and 92.33% dye reduction of 339 mg/L dye were achieved. These values are equal to overall 94.85% dye reduction of 500 mg/L, and 93.15% COD reduction of 380 mg/L. As a result, 500 mg/L dye was reduced to 26 mg/L, and 380 mg/L COD was reduced to 25 mg/L. The biodegradation fitted to Monod kinetics, for which kinetics parameter values of specific growth rate constant of biomass µ = 0.0047 h−1, yield coefficient (Y) = 1.059, and substrate utilization rate (q) = 0.0044 h−1 were evaluated at HRT = 2.5 d. The results show, this process can be applied to treat Acid Red 3BN Dye Water (AR3BNDW).

Water recovery and on-site reuse of laundry wastewater by a facile and cost-effective system: Combined biological and advanced oxidation process

Combined biological and physicochemical process was selected for treatment of laundry wastewater. The results show that after microbial adaptation, almost 91% of COD was removed at food to microorganism (F/M) ratio of 0.12 gBOD/gMLSS·d. Dehydrogenase activity of the biomass showed an increasing trend and finally reached 3.8 μgTFgbiomass.d corresponding to the highest process performance. 16SrRNA fragment and phylogenetic analysis identified Pseudomonas pharmacofabricae and Bacillus spp. as the dominant bacteria. The effluent of the biological process was then injected into the UV/O3 process for complete removal of residual COD and detergent. Finally, microfiltration and ultrafiltration were used to remove any remaining suspended solids. The operating cost analysis showed that 0.65 €/m3 treated wastewater is required for treatment of the laundry wastewater. Accordingly, the suggested combination of the biological and physicochemical process could be a promising and highly efficient process for treatment and reuse of laundry wastewater.

Effects of NaOH, thermal, and combined NaOH-thermal pretreatments on the biomethane yields from the anaerobic digestion of walnut shells

Anaerobic digestion (AD) of walnut shells (WS) results in only a limited biomethane yield because of their high fibre content, which ultimately represents an essentially nonbiodegradable lignocellulosic biomass. In the present study, thermal (i.e. 50-250 °C), alkaline (i.e. 1-5% w/w NaOH) and combined alkaline-thermal (i.e. 4% w/w NaOH + 150 °C thermal) pretreatment methods have been applied to increase the anaerobic biodegradation of WS. The highest biomethane yields of 159.9 ± 6.8 mL CH₄.g VS^-1 and 169.8 ± 6.8 mL CH₄.g VS^-1 were achieved after pretreatment at both 250 °C and with 4% NaOH. After combined NaOH-thermal pretreatments, the AD process showed the largest total VFA concentration (i.e. 1280.1 mg Hac L^-1) but a relatively high lag phase (i.e. 3.90 days) compared to thermal and NaOH pretreatments alone, from which the highest biomethane yield (i.e. 192.4 ± 8.2 mL CH₄.g VS^-1 ) was achieved at the end of the AD process. The highest biomethane yield from the combined NaOH-thermal pretreated WS was corroborated by the corresponding highest SCOD/TCOD ratio (i.e. 0.37 ± 0.02) and the highest lignocellulosic fibre removal (i.e. 41.1 ± 2.7% cellulose, 35.6 ± 1.8% hemicellulose, and 58.7 ± 3.2% lignin). The cumulative biomethane yields were further simulated via a modified Gompertz model. This study provides a promising strategy in the sense that the biomethane yield of WS containing large amounts of lignin can be significantly increased via thermal, NaOH, and combined NaOH-thermal pretreatment methods.

The upgrading of conventional activated sludge processes with thermophilic aerobic membrane reactor: Alternative solutions for sludge reduction

Sludge recovery/disposal represents one of the most crucial aspects related to the management of wastewater treatment plants. The most widely diffused technology for the treatment of industrial and municipal wastewaters is the conventional activated sludge (CAS) process, which is characterized by a relatively high excess sludge production. Different technical solutions are proposed in the literature for sludge minimization and they can be applied either on wastewater line (WL) or sludge line (SL). This work is focused on different approaches based on the use of Thermophilic Aerobic Membrane Reactor (TAMR): this can be added to a CAS plant, and integrated to WL or SL, yielding a significant sludge reduction. The process performance was analysed in terms of volatile solids (VS) reduction and specific sludge production. The TAMR was tested both at full-scale and pilot-scale with different feeding substrates: industrial wastewater for the full-scale plant; industrial wastewater, sludge and a mix of these for the pilot-scale plants. The results obtained are: (i) good solids removal (38-90% and 40-50% in terms of VS for sludge and mix of industrial wastewater and sludge, respectively), (ii) low specific sludge production (0.01-0.09 kg_{VSS produced} kg_{COD removed}^-1 for industrial wastewater and 0.014-0.069 kg_{VSS produced} kg_{COD removed}^-1 for mix of industrial wastewater and sludge) and (iii) a significant reduction of sludge when CAS is improved with the TAMR technology.

Investigation of the process stability of different anammox configurations and assessment of the simulation validity of various anammox-based kinetic models

Over the last 30 years, the successful implementation of the anammox process has attracted research interest from all over the world. Various reactor configurations were investigated for the anammox process. However, the construction of the anammox process is a delicate topic in regards to the high sensitivity of the biological reaction. To better understand the effects of configurations on the anammox performance, process-kinetic models and activity kinetic models were critically overviewed, respectively. A significant difference in the denitrification capabilities was observed even with similar dominated functional species of anammox with different configurations. Although the kinetic analysis gained insight into the feasibility of both batch and continuous processes, most models were often applied to match the kinetic data in an unsuitable manner. The validity assessment illustrated that the Grau second-order model and Stover–Kincannon model were the most appropriate and shareable reactor-kinetic models for different anammox configurations. This review plays an important role in the anammox process performance assessment and augmentation of the process control.

Over the last 30 years, the successful implementation of the anammox process has attracted research interest from all over the world.

Performance evaluation and substrate removal kinetics in an up-flow anaerobic hybrid membrane bioreactor treating simulated high-strength wastewater

The prime objective of the present study is to evaluate the performance of novel up-flow anaerobic hybrid membrane bioreactor (An-HMBR) treating high-strength wastewater (synthetic) using polyurethane foam as filter media. Treatment efficiency of the entire An-HMBR varied from 88-97% corresponding to 0.67-3.90 d of hydraulic retention time (HRT) with organic loading rate of 6.4-1.06 kg COD m^-3 d^-1. The modified Stover-Kincannon model was the most appropriate model for An-HMBR and anaerobic hybrid bioreactor (excluding membrane). The suspended growth system in An-HMBR could be described by both modified Stover-Kincannon and Grau second order model. The attached growth system in An-HMBR followed conventional Monod's kinetics. A novel combination of suspended, attached and membrane in single reactor increased the solid retention time to as high as 756 d at 3.9 d HRT which not only improved the COD removal efficiency but also enhanced the performance of the membrane.

Biological treatment of slaughterhouse wastewater: kinetic modeling and prediction of effluent

In this study three modeling approaches consisting Modified Stover-Kincannon, multilayer perceptron neural network (MLPANN) and B-Spline quasi interpolation were applied in order to predict effluent of up-flow anaerobic sludge blanket (UASB) reactor and also to find the reaction kinetics. At first run, the average total chemical oxygen demand (TCOD) removal efficiency was 48.3% with hydraulic retention time (HRT) of 26 h and 63.8% with HRT of 37 h, at OLR of 0.77-1.66 kg TCOD/m³ d. At the second run, UASB reactor operated with OLR of 1.94-3.1 kg TCOD/m³ d and achieved the average TCOD removal efficiency of 64.74 and 72.48% with HRT of 26 and 37 h, respectively. The Modified Stover-Kincannon performed well in terms of kinetic determination with a high value of regression coefficient over 0.98. The B-Spline quasi interpolation and MLPANN indicated a great fit for effluent prediction with average R of 0.9984 and 0.9986, and MSE of 157.6050 and 129.7796, respectively; however, they gave no information about reactions occurred in the system.

Investigation of growth kinetics and partial denitrification performance in strain Acinetobacter johnsonii under different environmental conditions

A denitrifying strain ZY04 with a high nitrite-accumulating rate was isolated and purified from activated sludge in a laboratory-scale A2/O reactor. The strain was characterized and identified as Acinetobacter johnsonii by 16S rDNA phylogenetic analysis. The sequences of the key functional genes (napA, nirB, nirD) involved in partial denitrification were amplified via polymerase chain reaction, which provided a basis for exploring gene expression. The effects of different environmental factors (C/N ratio, pH and temperature) on the partial denitrification performance and transcriptional levels of the functional genes during the logarithmic growth phase were investigated by batch experiments. The results showed that the partial denitrification performance was optimal when the C/N ratio was 5, the pH value was 6-8 and the temperature was 25°C. The gene expression during the logarithmic growth phase indicated the good performance of partial denitrification under different environmental conditions. All three functional genes exhibited the highest expression levels at 25°C. The results of inhibitory kinetics analysis revealed that three biokinetic models (Aiba, Edwards and Andrews) simulated the growth pattern of strain ZY04 inhibited by a single substrate (nitrate or sodium acetate) well. In the double-substrate inhibitory model, five models of nine combinations successfully fitted the growth characteristics of the strain affected by the double substrate of nitrate and sodium acetate. The relevant semi-saturation parameters and substrate inhibition parameters were obtained, and the correlation coefficient (R 2) reached 98%.

Investigation of Temperature Effect on Start-Up Operation from Anaerobic Digestion of Acidified Palm Oil Mill Effluent

Malaysia is one of the largest palm oil producers worldwide and its most abundant waste, palm oil mill effluent (POME), can be used as a feedstock to produce methane. Anaerobic digestion is ideal for treating POME in methane production due to its tolerance to high-strength chemical oxygen demand (COD). In this work, we compared the culture conditions during the start-up of anaerobic digestion of acidified POME between thermophilic (55 °C) and mesophilic (37 °C) temperatures. The pH of the digester was maintained throughout the experiment at 7.30 ± 0.2 in a working volume of 1000 mL. This study revealed that the thermophilic temperature stabilized faster on the 44th day compared to the 52nd day for the mesophilic temperature. Furthermore, the thermophilic temperature indicated higher biogas production at 0.60 L- CH 4 /L·d compared to the mesophilic temperature at 0.26 L- CH 4 /L·d. Results from this study were consistent with the COD removal of thermophilic temperature which was also higher than the mesophilic temperature.

Multi-agent simulation regulated by microbe-oriented thermodynamics and kinetics equations for exploiting interspecies dynamics and evolution between methanogenesis, sulfidogenesis, hydrogenesis and exoelectrogenesis

Multi-agent simulation (MAS) regulated by microbe-oriented thermodynamics and kinetics equations were performed for exploiting the interspecies dynamics and evolution in anaerobic respiration and bioelectrochemical systems. A newly-defined kinetically thermodynamic parameter is recognized microbes as agents in various conditions, including electron donors and acceptors, temperature, pH, etc. For verification of the MAS, the treatment of synthetic wastewater containing glucose and acetate was evaluated in four 25°C laboratory-scale reactors with different electron acceptors and cathode materials that had potential for methanogenesis, hydrogenesis, sulfidogenesis and exoelectrogenesis. Within 1000 h operation, the reactors performance and microbial structures using 16S rRNA sequencing matched with the MAS, suggesting acetoclastic exoelectrogenesis predominance (Geobacter). After 2400 h, MAS observed the co-existence of acetoclastic methanogenesis and acetoclastic and propionate exoelectrogenesis, as was reported previously. Such microbial evolution from the short-term to long-term operation likely resulted from the glucose-driven propionate. The MAS developed is applicable in a wide range of complex engineering and natural ecosystems.

Optimization of organic matter degradation kinetics and nutrient removal on artificial wetlands using Eichhornia crassipes and Typha domingensis

This study describes the optimization of the wastewater treatment process through the use of a free water surface flow constructed wetland with floating macrophytes at the laboratory level (20 L). A factorial design 2³ was used in order to find the best operation conditions of the wastewater treatment process. The performance of macrophytes Eichhornia crassipes and Typha domingensis was investigated by operating the wetland system at hydraulic retention times of 2 and 4 days. The results showed an optimum operational condition that removed 92.39% of initial organic load (measured as COD). The nutrient removal efficiency of the constructed wetland was 99.28% for total nitrogen and 87.78% for phosphorus. The best operating condition includes the use of E. crassipes, with 4 days of hydraulic retention and the use of gravel as a filter. According to this, organic matter degradation kinetics was studied by the comparison of three kinetic models: first-order model, Stover-Kincannon model and Grau-second-order model. Stover-Kincannon and Grau kinetics models were more appropriate to represent the organic matter degradation kinetics in constructed wetland, with a determination coefficient of 0.9997. Based on the kinetic removal results, the process showed a maximum rate of organic load removal of 2500 mg/L d.

Modelling anaerobic, aerobic and partial nitritation-anammox granular sludge reactors - A review

Wastewater treatment processes with granular sludge are compact and are becoming increasingly popular. Interest has been accompanied by the development of mathematical models. This contribution simultaneously reviews available models in the scientific literature for anaerobic, aerobic and partial nitritation-anammox granular sludge reactors because they comprise common phenomena (e.g. liquid, gas and granule transport) and thus pose similar challenges. Many of the publications were found to have no clearly defined goal. The importance of a goal is stressed because it determines the appropriate model complexity and helps other potential users to find a suitable model in the vast amount of literature. Secondly, a wide variety was found in the model features. This review explains the chosen modelling assumptions based on the different reactor types and goals wherever possible, but some assumptions appeared to be habitual within fields of research, without clear reason. We therefore suggest further research to more clearly define the range of operational conditions and goals for which certain simplifying assumptions can be made, e.g. when intragranule solute transport can be lumped in apparent kinetics and when biofilm models are needed, which explicitly calculate substrate concentration gradients inside granules. Furthermore, research is needed to better mechanistically understand detachment, removal of influent particulate matter and changes in the mixing behaviour inside anaerobic systems, before these phenomena can be adequately incorporated in models. Finally, it is suggested to perform full-scale model validation studies for aerobic and anammox reactors. A spreadsheet in the supplementary information provides an overview of the features in the 167 reviewed models.

Design and development of a hybrid macrophyte assisted vermifilter for the treatment of dairy wastewater: A statistical and kinetic modelling approach

Global urbanization, exponential increase in population and sophisticated life style of the present generation are the major causes leading to a rapid increase in water demand in recent years. In order to nullify this rising water demand, it's high time to reuse domestic as well as industrial effluent after providing suitable chemical/biological treatment. Macrophyte filter incorporated with earthworm is identified as one of the most economic system for the treatment purpose in developing countries. However, very few literatures and technical information are available to scale up the design and its easy operation. This paper aims to develop a hybrid system and assess its performance for the purification of dairy wastewater. In the present study, two stage macrophyte assisted vermifilters (MAVFs) have been designed. The 1st stage encompassed a vertical flow (VF) unit, and the 2nd stage contained a horizontal flow (HF) unit. Both the units were inoculated with earthworm Eisenia fetida and were planted with Canna indica. Box-Behnken model was applied to design the system and study the effect of various parameters. It was observed that hybrid MAVF system removed a maximum of 83.2% COD and 57.3% TN at HLR 0.6 m/d and an active layer depth of 30 cm. Ammonification and nitrification typically occurred in the active layer (earthworm inoculated zone) of VF unit due to high activity of earthworms and its associated gut microbes, whereas HF unit facilitate denitrification process. Earthworm growth characteristics in the system were monitored, which is an imperative factor for the design of MAVF reactor. Kinetic modelling of 1st order, grau 2nd order and Stover-Kincannon model were performed and the Stover-Kincannon model showed high regression coefficient (COD, R² 0.9961 and TN, R² 0.9353) supporting its applicability as compared to the other models.

Up-flow constructed wetland-microbial fuel cell for azo dye, saline, nitrate remediation and bioelectricity generation: From waste to energy approach

This study explored the influence of azo dye concentration, salinity (with and without aeration) and nitrate concentration on bioelectricity generation and treatment performance in the up-flow constructed wetland-microbial fuel cell (UFCW-MFC) system. The decolourisation efficiencies were up to 91% for 500 mg/L of Acid Red 18 (AR18). However, the power density declined with the increment in azo dye concentration. The results suggest that the combination of salinity and aeration at an optimum level improved the power performance. The highest power density achieved was 8.67 mW/m². The increase of nitrate by 3-fold led to decrease in decolourisation and power density of the system. The findings revealed that the electron acceptors (AR18, nitrate and anode) competed at the anodic region for electrons and the electron transfer pathways would directly influence the treatment and power performance of UFCW-MFC. The planted UFCW-MFC significantly outweighed the plant-free control in power performance.

Sequential anaerobic-aerobic treatment using plant microbe integrated system for degradation of azo dyes and their aromatic amines by-products

The presence of unused dyes and dye degradation intermediates in the textile industry wastewaters is the major challenge in its treatment. A wide range of treatments including various physicochemical processes are used for this wastewater. Incomplete dye degradation results in hazardous colorless aromatic amine intermediates that are teratogenic in nature. A synergistic plant-microbe system operated in a sequential anaerobic-aerobic mode was evaluated for the complete degradation of a model azo dye methyl red under laboratory conditions. The degradation of methyl red and its break down products 2-aminobenzoic acid and N,N-dimethyl-p-phenylenediamine were analysed by HPLC, FTIR and GC-MS. The vetiver-microbe system had shown enhanced dye degradation. The dye decolourization percentage achieved for integrated plant-microbe treatment system (T) after anaerobic condition was 53.5 ± 6.2% and aerobic condition was 92 ± 3.4%. The removal efficiency of the intermediates 2-ABA and DMPD was found to be 89.79% in the integrated plant-microbe treatment system. The plant-microbe system was most effective in the removal of toxic aromatic amine as seen by lesser phytotoxicity for seed germination and teratogenicity in case of zebrafish development in the treated water.

Biodegradation of textile wastewater: enhancement of biodegradability via the addition of co-substrates followed by phytotoxicity analysis of the effluent

This work reports on the biodegradation of textile wastewater by three alternative microbial treatments. A bacterial consortium, isolated from a dyeing factory, showed significant efficacy in decolourizing wastewater (77.6 ± 3.0%); the decolourization rate was 5.80 ± 0.31 mg of azo dye·L^-1·h^-1, without the addition of an ancillary carbon source (W). The degradation was 52% (measured as COD removal) and the products of the treatment showed low biodegradability (COD/BOD₅ = 4.2). When glucose was added to the wastewater, (W + G): the decolourization efficiency increased to 87.24 ± 2.5% and the decolourization rate significantly improved (25.67 ± 3.62 mg·L^-1·h^-1), although the COD removal efficiency was only 44%. Finally, the addition of starch (W + S) showed both a similar decolourization rate and efficiency to the W treatment, but a higher COD removal efficiency (72%). In addition, the biodegradability of the treated wastewater was considerably improved (COD/BOD₅ = 1.2) when starch was present. The toxicity of the degradation products was tested on Lactuca sativa seeds. In all treatments, toxicity was reduced with respect to the untreated wastewater. The W + S treatment gave the best performance.

Performance and kinetic evaluation of an integrated anaerobic-aerobic bioreactor in the treatment of palm oil mill effluent

This work presents the evaluation of biokinetic coefficients for a novel integrated anaerobic-aerobic bioreactor (IAAB) at different organic loading rates (OLRs) (10.5-22.5 g COD/L per day) treating palm oil mill effluent. The overall efficiencies of the chemical oxygen demand (COD) and biochemical oxygen demand (BOD) were more than 99% for OLR up to 19.5 g COD/L day with biogas production containing 48-64% of methane. The effluent quality remained stable (BOD < 80 mg/L) and satisfied with the discharge limit. Stover-Kincannon model was the most appropriate model to estimate the performance of anaerobic compartment of IAAB, while Monod model was best suited for describing the aerobic compartment.

ABBREVIATIONS

BOD: biochemical oxygen demand; COD: chemical oxygen demand; DO: dissolved oxygen; GLSS: gas-liquid-solid separator; MLSS: mixed liquor suspended solid; MLVSS: mixed liquor volatile suspended solid; POME: palm oil mill effluent; RAS: returned activated sludge; SBR: sequencing batch reactor; SVI: sludge volume index; TA: total alkalinity; TN: total nitrogen; TS: total solids; TSS: total suspended solids; UASB: upflow anaerobic sludge blanket; UASFF: upflow anaerobic sludge blanket fixed film; VFA: volatile fatty acid; VSS: volatile suspended solids.

Four-stage biofilm anaerobic–anoxic–oxic–oxic system for strengthening the biological treatment of coking wastewater: COD removal behaviors and biokinetic modeling

Biokinetic models of high-strength coking wastewater with a high chemical oxygen demand (COD) was efficiently treated by a novel pilot-scale four-stage biofilm anaerobic–anoxic–oxic–oxic (FB-A²/O²) system.

The Comparative Study on the Rapid Decolorization of Azo, Anthraquinone and Triphenylmethane Dyes by Anaerobic Sludge

An anaerobic sludge (AS), capable of decolorizing a variety of synthetic dyes, was acclimated and is reported here. The sludge presented a much better dye decolorizing ability than that of different individual strains. A broad spectrum of dyes could be decolorized by the sludge. Continuous decolorization tests showed that the sludge exhibited the ability to decolorize repeated additions of dye. The chemical oxygen demand (COD) removal rate of the dye wastewater reached 52% after 12 h of incubation. Polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) profiles revealed that the microbial community changed as a result of varying initial concentrations of dyes. Phylogenetic analysis indicated that microbial populations in the sludge belonged to the phyla Acidobacteria, Firmicutes, Bacteroidetes, Chloroflexi and Proteobacteria. The degradation products of the three types of dye were identified. For azo dyes, the anaerobic sludge converted Methyl Orange to N,N-dimethylbenzene-1,4-diamine and 4-aminobenzenesulfonic acid; for triphenylmethane dyes, after Malachite Green was decolorized, the analyzed products were found to be a mixture of N,N-dimethylbenzenamine, 3-dimethyl-aminophenol and 4-dimethylaminobenzophenone; for anthraquinone dyes, two products (acetophenone and 2-methylbenzoic acid) were observed after Reactive Blue 19 decolorization. Together, these results suggest that the anaerobic sludge has promising potential for use in the treatment of industrial wastewater containing various types of dyes.

Pilot test of biological removal of 1,4-dioxane from a chemical factory wastewater by gel carrier entrapping Afipia sp. strain D1

A pilot-scale (120 L) bioreactor system using a gel carrier-entrapped pure bacterial strain, Afipia sp. strain D1, capable of degrading 1,4-dioxane as a sole carbon and energy source was constructed and applied to treat real industrial wastewater containing 1,4-dioxane from a chemical factory. Although the wastewater not only contained high concentrations of 1,4-dioxane but also considerable amounts of other organic compounds (73 mg-TOCL(-1) on average), the bioreactor could efficiently remove 1,4-dioxane without significant inhibitory effects. The reactor startup could be completed within approximately 1 month by increasing the 1,4-dioxane loading rate (0.09-0.47 kg-dioxanem(-3)d(-1)) in a stepwise manner. Effective 1,4-dioxane removal was stably maintained for 3 months with an influent 1,4-dioxane of 570-730 mg L(-1), giving an average effluent concentration and removal rate of 3.4 mg L(-1) and 0.46 kg-dioxanem(-3)d(-1), respectively. A 1,4-dioxane loading fluctuation between 0.14 and 0.72 kg-dioxanem(-3)d(-1) did not significantly affect its removal, and more than 99% removal efficiency was constantly maintained. The Monod model could well describe the relationship between the effluent 1,4-dioxane concentration and 1,4-dioxane removal rates of the bioreactors, showing that the half-saturation constant (Ks) was 28 mg L(-1).

Sequential UASB and dual media packed-bed reactors for domestic wastewater treatment - experiment and simulation

A wastewater treatment system composed of an upflow anaerobic sludge blanket (UASB) reactor followed by a packed-bed reactor (PBR) filled with Sorbulite(®) and Polonite(®) filter material was tested in a laboratory bench-scale experiment. The system was operated for 50 weeks and achieved very efficient total phosphorus (P) removal (99%), 7-day biochemical oxygen demand removal (99%) and pathogenic bacteria reduction (99%). However, total nitrogen was only moderately reduced in the system (40%). A model focusing on simulation of organic material, solids and size of granules was then implemented and validated for the UASB reactor. Good agreement between the simulated and measured results demonstrated the capacity of the model to predict the behaviour of solids and chemical oxygen demand, which is critical for successful P removal and recovery in the PBR.

Evaluation of the treatment performance of lab-scaled vertical flow constructed wetlands in removal of organic compounds, color and nutrients in azo dye-containing wastewater

The objective of this study is to examine the treatment performance of vertical flow intermittent feeding constructed wetland (VFCW) in removal of organic pollution, nutrients and color in azo-dye containing wastewater. The systems consisted of PVC reactors, some filling materials such as gravel, sand and zeolite and wetland plants including Typha angustifolia and Canna indica. The average treatment efficiency of the systems for COD, color, sulphate, NH4-N, and PO4-P were in the range of 57-63%, 94-99%, 44-48%, 39-44%, and 84-88%, respectively among the VFCW reactors. It is concluded that VFCW reactor system can effectively be used in the treatment of dye-rich wastewater, especially for the removal of color and in the reduction of COD. Biofilm formation and cleavage of azo bonds could be observed by SEM and FTIR results, respectively. Almost similar NH4-N and PO4-P removal were obtained in all reactors by using same amount of zeolite media.

Performance and modeling of a moving bed biofilm process: nickel and chromium heavy metal removal from industrial wastewater

The process of a lab-scale moving bed biofilm reactor (MBBR) using simulated sugar-manufacturing wastewater as feed was investigated.

Kinetics Study of UASB and HUASB System in Treating Municipal Wastewater

. A combined laboratory-scale system UASB-DFAF and HUASB-DFAF was operated for treating Municipal wastewater at six hydraulic retention times (HRT) of 45.08, 30.06, 22.54, 18.03, 15.03, 12.88 h. COD removal efficiency in range from 72% to 82% in UASB, while in HUASB range from 84 to 89% with decrease of HRT. There are several method have been developed to represent biodegration of municipal sewerage in a combined treatment system. The Monod, Grou second-order and first order model have been used to analyze this studies. The combined of HUASB reactor, 5.41 L working volume, followed by DFAF reactor, having a working volume 2.67L were analyzed. The kinetic parameters were determined through line regression using experimental data. The predicted COD concentration was calculated using the kinetic constant. The kinetic models applied for this study were Grou second-order, followed by first order method and Monod method.

Mineralization of reactive azo dyes present in simulated textile waste water using down flow microaerophilic fixed film bioreactor

The present research emphasizes on degradation of azo dyes from simulated textile wastewater using down flow microaerophilic fixed film reactor. Degradation of simulated textile wastewater (COD 7200mg/L and dye concentration 300mg/L) was studied in a microaerophilic fixed film reactor using pumice stone as a support material under varying hydraulic retention time (HRT) and organic loading rate (OLR). The intense metabolic activity of the inoculated bacterial consortium in the reactor led to 97.5% COD reduction and 99.5% decolorization of simulated wastewater operated under OLR of 7.2kgCODm(3)/d and 24h of HRT. FTIR, (1)H NMR and GC-MS studies revealed the formation of lower molecular weight aliphatic compounds under 24h of HRT, leading to complete mineralization of simulated wastewater. The detection of oxido-reductive enzyme activities suggested the enzymatic reduction of azo bonds prior to mineralization. Toxicity studies indicated that microbial treatment favors detoxification of simulated wastewater.

Performance and kinetic process analysis of an Anammox reactor in view of application for landfill leachate treatment

Anammox has shown its promise and low cost for removing nitrogen from high strength wastewater such as landfill leachate. A reactor was inoculated with nitrification-denitrification sludge originating from a landfill leachate treating waste water treatment plant. During the operation, the sludge gradually converted into red Anammox granular sludge with high and stable Anammox activity. At a maximal nitrogen loading rate of 0.6 g N l(-1) d(-1), the reactor presented ammonium and nitrite removal efficiencies of above 90%. In addition, a modified Stover-Kincannon model was applied to simulate and assess the performance of the Anammox reactor. The Stover-Kincannon model was appropriate for the description of the nitrogen removal in the reactor with the high regression coefficient values (R2 = 0.946) and low Theil's inequality coefficient (TIC) values (TIC < 0.3). The model results showed that the maximal N loading rate of the reactor should be 3.69 g N l(-1) d(-).

Performance of ceramic ultrafiltration membranes and fouling behavior of a dye-polysaccharide binary system

Ultrafiltration membrane processes have become an established technology in the treatment and reuse of secondary effluents. Nevertheless, membrane fouling arises as a major obstacle in the efficient operation of these systems. In the current study, the performance of tubular ultrafiltration ceramic membranes was evaluated according to the roles exerted by membrane pore size, transmembrane pressure and feed concentration on a binary foulant system simulating textile wastewater. For that purpose, carboxymethyl cellulose sodium salt (CMC) and an azo dye were used as colloidal and organic foulants, respectively. Results showed that a larger pore size enabled more solutes to get adsorbed into the pores, producing a sharp permeate flux decline attributed to the rapid pore blockage. Besides, an increase in CMC concentration enhanced severe fouling in the case of the tighter membrane. Concerning separation efficiency, organic matter was almost completely removed with removal efficiency above 98.5%. Regarding the dye, 93% of rejection was achieved. Comparable removal efficiencies were attributed to the dynamic membrane formed by the cake layer, which governed process performance in terms of rejection and selectivity. As a result, none of the evaluated parameters showed significant influence on separation efficiency, supporting the significant role of cake layer on filtration process.

Utilization of moving bed biofilm reactor for industrial wastewater treatment containing ethylene glycol: kinetic and performance study

One of the requirements for environmental engineering, which is currently being considered, is the removal of ethylene glycol (EG) as a hazardous environmental pollutant from industrial wastewater. Therefore, in a recent study, a moving bed biofilm reactor (MBBR) was applied at pilot scale to treat industrial effluents containing different concentrations of EG (600, 800, 1200, and 1800 mg L-1 ). The removal efficiency and kinetic analysis of the system were examined at different hydraulic retention times of 6, 8, 10, and 12 h as well as influent chemical oxygen demand (COD) ranged between values of 1000 and 3000mg L-1. In minimum and maximum COD Loadings, the MBBR showed 95.1% and 60.7% removal efficiencies, while 95.9% and 66.2% EG removal efficiencies were achieved in the lowest and highest EG concentrations. The results of the reactor modelling suggested compliance of the well-known modified Stover-Kincannon model with the system.

Identical full-scale biogas-lift reactors (Blrs) with anaerobic granular sludge and residual activated sludge for brewery wastewater treatment and kinetic modeling

Two identical full-scale biogas-lift reactors treating brewery wastewater were inoculated with different types of sludge to compare their operational conditions, sludge characteristics, and kinetic models at a mesophilic temperature. One reactor (R1) started up with anaerobic granular sludge in 12 weeks and obtained a continuously average organic loading rate (OLR) of 7.4 kg chemical oxygen demand (COD)/(m3 x day), COD removal efficiency of 80%, and effluent COD of 450 mg/L. The other reactor (R2) started up with residual activated sludge in 30 weeks and granulation accomplished when the reactor reached an average OLR of 8.3 kg COD/(m3 x day), COD removal efficiency of 90%, and effluent COD of 240 mg/L. Differences in sludge characteristics, biogas compositions, and biogas-lift processes may be accounted for the superior efficiency of the treatment performance of R2 over R1. Grau second-order and modified StoverKincannon models based on influent and effluent concentrations as well as hydraulic retention time were successfully used to develop kinetic parameters of the experimental data with high correlation coefficients (R2 > 0.95), which further showed that R2 had higher treatment performance than R1. These results demonstrated that residual activated sludge could be used effectively instead of anaerobic granular sludge despite the need for a longer time.

Application and kinetic evaluation of upflow anaerobic biofilm reactor for nitrogen removal from wastewater by Anammox process

The lab-scale upflow anaerobic biofilm reactor was successfully operated for the treatment of synthetic wastewater with high nitrogen load by Anammox (anaerobic ammonium oxidation) process. During the entire period of operation, the reactor temperature was kept at 35±1°C. The operational strategy consisted of both increasing the ammonium and nitrite concentrations from 60 to 700mgN/L and from 80 to 920 mgN/L, respectively and decreasing the hydraulic retention time from 24 to 6 h, at each step. The highest achieved removal efficiency of ammonium and nitrite were 91 and 93%, respectively. Consequently, due to their acceptable performance for nitrogen removal in previous researches, modified Stover-Kincannon and Grau second-order models were used in this study. According to the experiment results, the model validity testing showed that the Stover-Kincannon model was a little more appropriate for the description of nitrogen removal in the reactor, even though both models gave high correlation coefficients (R(2)=0.999).

Substrate removal kinetics in high-rate upflow anaerobic filters packed with low-density polyethylene media treating high-strength agro-food wastewaters

The process kinetics for two upflow anaerobic filters (UAFs) treating high strength fruit canning and cheese-dairy wastewaters as feed were investigated. The experimental unit consisted of a 10-L (effective volume) reactor filled with low-density polyethylene media. COD removal efficiencies of about 80% were recorded at the maximum OLRs of 19 and 17 g COD L(-1) d(-1) for the fruit canning and cheese-dairy wastewaters, respectively. Modified Stover-Kincannon and second-order kinetic models were applied to data obtained from the experimental studies in order to determine the substrate removal kinetics. According to Stover-Kincannon model, U(max) and K(B) values were estimated as 109.9 and 109.7 g L(-1) d(-1) for fruit canning, and 53.5 and 49.7 g L(-1) d(-1) for cheese dairy wastewaters, respectively. The second order substrate removal rate k(2(s)) was found to be 5.0 and 1.93 d(-1) respectively for fruit canning and cheese dairy wastewaters. As both these models gave high correlation coefficients (R(2) = 98-99%), they could be used in predicting the behaviour or design of the UAF.