Inlet COD Research Articles

Development of Palm Oil Plantation By-products in Sintang District to Support SISKA Program and Environmental Health

Abstract The study aims to explore the potential of utilizing palm oil plantation by-products, such as fronds, palm oil mill effluent (POME), and palm sludge, in the cattle palm integration program. The objective is to optimize the use of these by-products. The research area covers 18,600 hectares with a palm oil mill capacity of 60 tons FFB/hour. The plantation produces 20,944 tons of fronds per hectare annually, with 136 planting trees per hectare. The Palm Oil Mill Effluent (POME) has an inlet BOD of 25,000 - 35,000 mg/liter and inlet COD of 35,000 - 45,000 mg/liter. The palm sludge produced is 11,904 tons per year. All the remaining by products from palm oil plantations have the potential to be used as animal feed ingredients to support the cattle palm integration program (SISKA) to produce green economic cycle in addition to a green environment. However, to achieve this goal, further study is needed.

Sequential treatment of landfill leachate by electrocoagulation/aeration, PMS/ZVI/UV and electro-Fenton: Performance, biodegradability and toxicity studies

This study presents a systematic study on sequential treatment of highly resistant landfill leachate by electrocoagulation (EC)/aeration, sulfate radical advanced oxidation process (SR-AOP) and electro-Fenton (EF). In case of SR-AOP, peroxymonosulfate (PMS) catalyzed by zero valent iron (ZVI) and ultraviolet irradiation (UV) system was developed. Treatment process was optimized in respect to COD removal. Analysis of results revealed that sequential application of EC/aeration, PMS/ZVI/UV, and EF processes provide an extraordinary performance and meet the environmental regulations. The source of iron for EF process was provided from previous process reducing the cost of sequential process. Separately, EC/aeration (inlet COD = 4040 mg/L), PMS/ZVI/UV (inlet COD = 1560 mg/L), and EF (inlet COD = 471 mg/L) removed 61, 69 and 82% of COD respectively. Overall, sequential processes of EC/aeration, PMS/ZVI/UV and EF could remove the COD, TOC and ammonia of the landfill leachate around 98%, 93% and 94%, respectively. The comparison of different sequences of following processes indicated that current configuration (EC/aeration-PMS/ZVI/UV-EF) could meet the discharge standards. Furthermore, humification degree was significantly improved after oxidative processes. Biodegradability study was also performed by means of BOD/COD, average oxidation state (AOS), and Zahn-Wellens test, and the best results associated with these indices were obtained 0.56, 2.37, and over 98%, respectively. Phytotoxicity of leachate was remarkably reduced and the final effluent can be considered as a non-phytotoxic wastewater.

Anaerobic digestion of rice straw pretreatment liquor without detoxification for continuous biogas production using a 100 L internal circulation reactor

The production of biogas from lignocellulose by anaerobic digestion (AD) has attracted much attention recently. However, the over-acidification phenomenon and low biogas yield often occur during the AD of lignocellulose. In this work, the liquid-state fermentation mode using pretreatment liquor from dilute acid treated rice straw without detoxification for continuous biogas production in a 100 L internal circulation reactor was studied. The highest biogas yield reached 0.66 m3/kg CODconsumption while the methane yield was 0.38 m3/kg CODconsumption. The pH values of outlet were maintained at 6.9–7.4, and even the inlet pH values were lower than 6.0. Furthermore, from the second day to the end of fermentation, the COD removal rates were more than 90%, even though the inlet COD was close to 20000 mg/L. The organic substances from acid pretreated rice straw were efficiently degraded by AD, which was confirmed by substrate metabolism analysis. These results indicated that the whole fermentation process of AD was very stable and showed great potential for industrial application.

Fate and inhibition of Bis (2-Ethylhexyl) phthalate in biophysical reactors for treating real landfill leachate

In this study, the performance of combined Non-Thermal Plasma ( as a pre-treatment) and granular sludge sequencing batch reactor ( as a post-treatment) was evaluated for decontamination of real landfill leachate containing Bis (2-Ethylhexyl) phthalate. Special emphasis was placed on the biodegradability of leachate due to its high chemical stability and generation of intermediate species. A plasma reactor with a useful volume of 0.5 L, quartz material was utilized by this study for the pre-treatment process. The biological treatment efficiency was investigated using three granular sludge sequencing batch reactors, each containing 1.2 L with different apparatuses. The Hamadan landfill leachate sample was diluted with synthetic wastewater at 20%, 50%, and 100% v/v ratios. The applied influent Bis (2-Ethylhexyl) phthalate concentrations were 2, 4, 6, 8, 10, 15, and 20 mg/l. Organic loading rate in terms of COD and Bis (2-Ethylhexyl) phthalate concentrations, as well as reactor hydraulic retention time, were worked out to assess the processes performance (COD, nitrogen, phosphorus, and Bis (2-Ethylhexyl) phthalate removal efficiencies). Total Organic Carbon and 5-day Biochemical Oxygen Demand were also measured at the influent and effluent of the NTP reactor over a range of retention time (5, 10, 15, 20, 30, 45, and 60 min) to determine the degree of biodegradability enhancement. Cell protein concentration was also measured using a nanotherape device to assess the effect of DEHP inhibitor on bacterial growth. The main results arrived at from the overall assessment of the processes are that the BOD5/COD ratio of Non-Thermal Plasma reactor effluent at all leachate dilution, i.e., 20%, 50%, and 100% (v/v ratios) considerably increased, reaching 1.09 as compared to 0.33 in the raw influent. The findings indicated that the longer hydraulic retention time affected the granular sludge sequencing batch reactor efficiency. Further, cell protein concentration decreased by increasing the leachate contribution of inlet COD and increased Bis (2-Ethylhexyl) phthalate. It is concluded that Non-Thermal Plasma, as a highly competitive waste treatment technology coupled with aerobic granular sludge, could be considered for the biodegradation of landfill leachate containing chemically stable and recalcitrant organics not treatable by conventional techniques.

A case study on pulp and paper industry effluent treatment

Industrial effluent Management is one of the major environmental concerns, especially in developing countries under rapid industrialization. The grossly polluting industries recognized by Central Pollution Control Board (CPCB), such as Pulp and Paper Industries, poses even bigger environmental threats, owing to quantity and quality of effluent generated. This paper aimed at analyzing effluent management practices in pulp and paper industries in India, and asses the performance variability of a paper mill effluent treatment plant (ETP), as a Case Study. Majority of pulp and paper industries found to still employ conventional methods of effluent treatment. Although, most of the parameters of treated effluent are commonly reported within CPCB’s permissible discharge limits, the treatment is usually cost and energy intensive, and produce high amount of solid residuals as sludge. For the case study paper mill ETP, the treatment efficiencies of the ETP units were analyzed under variable inlet pH, TSS, TDS, BOD and COD loads. The pH variations in the range of 6.5 to 9 had little effect of COD or TSS removal, however removal efficiencies were higher for larger inlet COD or TSS loads. The results of the study could be helpful in optimizing operation of the existing ETPs, as well as, guiding on upgrading ETPs with more cost-effective and efficient units.

Biogas recovery from fresh landfill leachates by using a coupled air stripping-up follow anaerobic sludge blanket (UASB) process

The present study focuses on fresh leachates treatment using anaerobic digestion. To overcome the unsuitable raw characteristics, appropriate pretreatment conditions were identified based on Batch tests. A subsequently optimized pretreatment-anaerobic two stages UASB coupled treatment was studied. The performance of the overall coupled treatment was assessed by monitoring volatile fatty acids (VFA), COD and ammonium removal, and biogas performance. Results showed that combining acidity correction to short aeration gives a synergetic effect and allowed appropriate anaerobic start-up conditions. Under continuous aerobic pretreatment-UASB digestion, significant removal of NH+4 (75.87%), COD (19.14%), and VFA (20.3%) were achieved during the aeration step resulting in the total abatement of 88.66%, 83.6% and 70.39% for NH+4, COD, and VFA, respectively. The process allowed good biogas performance up to 2,470 mL biogas/L and 123 mL CH4/gCOD removed, with gradual improvement from the first to the second UASB reactor. Inlet COD and VFA feeding rate seemed to be the main key parameters with 45.37 g COD/L.d and 18.43 g VFA/L.d as a critical threshold. Therefore, the anaerobic digestion of high COD leachates is highly feasible and the aerobic–anaerobic coupled treatment is a promising technical scenario that deserves further studies.

Comparative evaluation of the sludge characteristics along the height of upflow anaerobic sludge blanket coupled ultrafiltration systems

This study provides a comparison of the sludge characteristics along the height of an upflow anaerobic sludge blanket (UASB) reactor in terms of sludge morphology, activity and stability. The main aim of this study was to identify the best location (i.e. where sludge is of lowest stability and/or highest concentration) in the sludge bed for conveying the sludge from the low temperature UASB reactor to a digester. The sludge profile was investigated by collecting sludge samples along the different heights of the UASB-anaerobic membrane bioreactor treating municipal wastewater. Results showed that total solids and volatile solids concentrations decreased with height, and the highest chemical oxygen demand concentration was observed at the bottom of the reactor. Active biomass remained near inlet of the reactor; whereas, non-active biomass consisted of loose, suspended particles and flocculents moved towards the top. This was confirmed by the high specific COD consumption rate near the inlet and poor specific COD biodegradation in the remaining portions of the bioreactor. Apparently, the assumption of a completely mixed sludge bed behavior for the UASB reactor, being part of an AnMBR system, does not hold for this type of reactor systems even at low temperatures, which makes the location in sludge bed from where the sludge is to be conveyed to the digester of operational importance. Considering the observed sludge bed stratification, the sludge to be recirculated from the UASB reactor to the digester is recommended to be taken from 40 to 50% of the sludge bed height.

Design and testing of a pilot-scale submerged membrane bioreactor (MBR) for textile wastewater treatment

The objective of this paper is to deal with the design of a pilot-scale submerged membrane bioreactor (MBR) and a short-term functionality test to be performed with textile wastewater. The design calculations were done based on the design parameters analysed from local textile wastewater and typical values of activated sludge kinetic coefficients. Other process parameters like bioreactor volume (tank size), hydraulic residence time (HRT), biomass loading (F/M ratio), oxygen demand, etc., were calculated depending on the real textile wastewater characteristics. Taking the design basis into consideration, a pilot-scale MBR was constructed equipped with LabVIEW programme- and sensors-controlled computer system. Based on the theoretical calculations, the hydraulic volume of the MBR reactor was around 56.6 L with flat sheet membranes (3 sheets, with 25 cm × 25 cm dimensions of each sheet) with HRT of 16.9 h. Finally, performance tests for 6 weeks were carried out in a local (Darmstadt, Germany) laundry textile wastewater to test the functionality of MBR pilot plant. Under the operating conditions of 250 mbar suction pressure and 12 g/L of MLSS, the COD removal efficiency was around 90% for 800–3500 mg/L inlet COD fed to the membrane bioreactor.

MFC-based biosensor for domestic wastewater COD assessment in constructed wetlands

In the context of natural-based wastewater treatment technologies (such as constructed wetlands - CW) the use of a low-cost, continuous-like biosensor tool for the assessment of operational conditions is of key importance for plant management optimization. The objective of the present study was to assess the potential use of constructed wetland microbial fuel cells (CW-MFC) as a domestic wastewater COD assessment tool. For the purpose of this work four lab-scale CW-MFCs were set up and fed with pre-settled domestic wastewater at different COD concentrations. Under laboratory conditions two different anodic materials were tested (graphite rods and gravel). Furthermore, a pilot-plant based experiment was also conducted to confirm the findings previously recorded for lab-scale experiments. Results showed that in spite of the low coulombic efficiencies recorded, either gravel or graphite-based anodes were suitable for the purposes of domestic wastewater COD assessment. Significant linear relationships could be stablished between inlet COD concentrations and CW-MFC Ecell whenever contact time was above 10 h. Results also showed that the accuracy of the CW-MFC was greatly compromised after several weeks of operation. Pilot experiments showed that CW-MFC presents a good bio-indication response between week 3 and 7 of operation (equivalent to an accumulated organic loading between 100 and 200 g COD/m2, respectively). Main conclusion of this work is that of CW-MFC could be used as an “alarm-tool” for qualitative continuous influent water quality assessment rather than a precise COD assessment tool due to a loss of precision after several weeks of operation.

Constructed wetlands for phytoremediation of industrial wastewater in Addis Ababa, Ethiopia

Brewery industries generate large amounts of wastewater rich in organic matter originating from the brewing process, and they are among the major polluting industries. This study aimed to assess the phytoremediation of brewery wastewater using horizontal subsurface flow constructed wetlands (HSFCWs) vegetated with Typha latifolia and Pennisetum purpureum for organics removal and plant growth analysis. Six parallel pilot-scale HSFCWs were constructed and operated to assess potential of treating wastewater sourced from St. George brewery factory located in Addis Ababa, Ethiopia. Three units were planted with T. latifolia and the other three with P. purpureum with one control without plants for each species. Primarily settled wastewater was fed evenly to them by gravity. Wastewater quality, plant growth analysis and system efficiency were observed during the experiment following standard methods. Both plants grew and established well, however, T. latifolia had more biomass and vigorous growth and showed good phytoremedial capacity to remove organic pollutants. Average removal efficiencies for BOD5 and COD were significant (p < 0.05), up to 87% (inlet BOD5 of 748–1642 mg l−1) and up to 81% (inlet COD of 835–2602 mg l−1) and T. latifolia slightly outperformed P. purpureum. Estimated biomass of significant (p < 0.05) value (0.61–0.86 kg DW m−2) was produced. HSFCWs are green and environmentally sustainable technology that offers promising alternative wastewater treatment method in developing countries of tropical climate due to its low-tech nature. Integrating treatment and biomass production needs further improvement.

Effect of Organic Loading Rates on biodegradation of linear alkyl benzene sulfonate, oil and grease in greywater by Integrated Fixed-film Activated Sludge (IFAS)

In this study, performance of Integrated Fixed-film Activated Sludge (IFAS) system in treatment of Linear Alkylbenzene Sulfonate (LAS), and oil & grease in synthetic greywater and effect of Organic Loading Rates (OLRs) on removal efficiency within a period of 105 days were investigated. Present study was carried out in a pilot scale under such conditions as temperature of 30 ± 1 °C, dissolved oxygen of 2.32 ± 0.91 mg/l, pH of 8.01 ± 0.95 and OLRs of 0.11–1.3gCOD/L.d. Also, Scanning Electron Microscopy (SEM) images were employed to specify rate of the biofilm formed on the media inside the reactor IFAS. The best removal efficiency for COD, LAS and oil and grease were respectively obtained as 92.52%, 94.24% and 90.07% in OLR 0.44gCOD/L.d. The assessment of loading rate indicated that with increased OLR to 0.44gCOD/L.d, removal efficiency of COD, oil and grease was increased while with increased OLR, removal efficiency was decreased. In doing so, based on the statistical test ANOVA, such a difference between removal efficiencies in diverse OLRs was significant for COD (p = 0.003), oil and grease (p = 0.01). However, in terms of LAS, with increased value of OLR to 0.44gCOD/L.d, the removal efficiency was increased and then with higher OLRs, removal efficiency was slightly decreased that is insignificant (p = 0.35) based on the statistical test ANOVA. The SEM images also showed that the biofilm formed on the media inside IFAS reactor plays a considerable role in adsorption and biodegradation of LAS, and oil & grease in greywater. The linear relation between inlet COD values and rate of removed LAS indicated that the ratio of inlet COD (mg/L) to removed LAS (mg/L) was 0.4. Therefore, use of IFAS system for biodegradation of LAS, oil and grease in greywater can be an applicable option.

Modeling of a UASB Reactor by NARX Networks for Biogas Production

Abstract An Artificial Neural Network model of a UASB Reactor has been developed. The reactor treats bagasse wash water (containing organics), generated after washing of stored bagasse prior to its use in paper manufacture. In the process, biogas, a renewable source of energy is produced. As the UASB reactors (2×5,000 m3 volume) operate mostly with feed having varying characteristics, therefore a special type of dynamic networks, called NARX networks have been used to model it for predicting biogas production rate. The input to the model is influent flow rate, inlet and outlet COD. Model is based upon 576 days plant data. NARX model architecture consists of input, output, and 2 hidden layers each having 10 neurons and utilizes 4 days delay. The developed ANN model represents the dynamic behavior of UASB reactor and recursively predicts and forecasts the biogas production rate with acceptable deviation with respect to actual production rate.

THE "CHEMICAL OXYGEN DEMAND / TOTAL VOLATILE ACIDS" RATIO AS AN ANAEROBIC TREATABILITY INDICATOR FOR LANDFILL LEACHATES

In some operational circumstances a fast evaluation of landfill leachate anaerobic treatability is necessary, and neither Biochemical Methane Potential nor BOD/COD ratio are fast enough. Looking for a fast indicator, this work evaluated the anaerobic treatability of landfill leachate from Sao Carlos-SP (Brazil) in a pilot scale Anaerobic Sequence Batch Biofilm Reactor (AnSBBR). The experiment was conducted at ambient temperature in the landfill area. After the acclimation, at a second stage of operation, the AnSBBR presented efficiency above 70%, in terms of COD removal, utilizing landfill leachate without water dilution, with an inlet COD of about 11,000 mg.L-1, a TVA/COD ratio of approximately 0.6 and reaction time equal to 7 days. To evaluate the landfill leachate biodegradability variation over time, temporal profiles of concentration were performed in the AnSBBR. The landfill leachate anaerobic biodegradability was verified to have a direct and strong relationship to the TVA/COD ratio. For a TVA/CODTotal ratio lower than 0.20, the biodegradability was considered low, for ratios between 0.20 and 0.40 it was considered medium, and above 0.40 it was considered high.

Kinetic coefficients for the domestic wastewater treatment using hybrid activated sludge process

In this study, the performance of a novel configuration of the hybrid growth bioreactor in pilot-plant scale (containing of anoxic, aerobic and sedimentation sections) was investigated for Isfahan municipal wastewater treatment plants. The bioreactor performance was evaluated after primary sedimentation tanks under the inlet COD concentration of 0.27±0.02 g/L, at different suspended biomass concentrations of about 3, 4, and 5 as g/L and different total hydraulic retention times 4, 8, and 12 h. An industrial moving bed packing with protected specific surface area of 350 m2/m3 was used in the bioreactor with a 30% of filling ratio. The modified Stover–Kincannon and Grau models are applied to predict the bio kinetic coefficients of COD removal. According to the results obtained, the substrate removal rate constant (ks) for Grau model was in the range of 8.23–10.96 (1/d), and the saturation constant (KB) value and the maximum total substrate utilization rate (Umax) for modified Stover–Kincannon were in the range of 57.4–87.7 (g/L d) and 62.6–91.4 (g/L d), respectively. Also, the results showed that the bioreactor follows the models with 98–99% correlation coefficients.

Explosive Propagation of Aeolosoma Hemprichi in an Activated Sludge-Biofilm Reactor

In order to understand the impact of the explosive propagation of aeolosoma hemprichi on the performance of an activated sludge-biofilm reactor at various temperature conditions, we conducted a beaker experiment and simulated the activated sludge-biofilm reactor, which is operated in a 1.0 L reactor with the filler dosing rate of 30% at 20oC, 25oC, and 30oC. We inoculate aeolosoma hemprichi after the activated sludgebiofilm reactor became steady, investigated whether and when the explosive propagation of aeolosoma hemprichi occurs at various ambient temperatures, and examined its impact on the performance of the activated sludge-biofilm reactor. The results show that the removal rate of ammonia nitrogen is basically stable at between 90-95%, and that of total nitrogen has remained at around 45% at 20oC. When the filler dosage rate is 30%, the removal rate of COD is stable between 85%-90%. The population density of aeolosoma hemprichi basically kept at 10 ind./mL, indicating that the aeolosoma hemprichi did not produce explosive reproduction. The explosive propagation of aeolosoma hemprichi occurs at the temperature of both 25oC and 30oC, while the maximum population densities of aeolosoma hemprichi are 383 ind./mL and 200 ind./mL, respectively. In addition, the explosive propagation has no impact on the removal rates of inlet and outlet COD and NH3-N, but it leads to an increase in the release rate of TN. Moreover, it is certified that the explosive propagation of aeolosoma hemprichi does not have an impact on the loss of biofilm. Finally, after multivariate regression analysis with SPSS, we concluded that the maximum population density of aeolosoma hemprichi has a significant correlation with the release rate of TN.

Pilot Research on Outer Loop EGSB Anaerobic Reactor for Pulping and Papermaking Wastewater

EGSB anaerobic reactor is used to treat the papermaking wastewater, and this paper explore the law of its quick start, HRT and operation cost. Results showed that, during the 47 days, at the condition of inlet COD concentration 2000mg/l, HRT 8h, ascending velocity 0.8m/h, gas output 3600L/d, the COD removal rate can reach up to 65%, and the operation cost is 0.75Yuan/t.

Experimental and theoretical characterization of microbial bioanodes formed in pulp and paper mill effluent in electrochemically controlled conditions

Microbial bioanodes were formed in pulp and paper effluent on graphite plate electrodes under constant polarization at -0.3 V/SCE, without any addition of nutriment or substrate. The bioanodes were characterized in 3-electrode set-ups, in continuous mode, with hydraulic retention times from 6 to 48 h and inlet COD from 500 to 5200 mg/L. Current densities around 4A/m(2) were obtained and voltammetry curves indicated that 6A/m(2) could be reached at +0.1 V/SCE. A theoretical model was designed, which allowed the effects of HRT and COD to be distinguished in the complex experimental data obtained with concomitant variations of the two parameters. COD removal due to the electrochemical process was proportional to the hydraulic retention time and obeyed a Michaelis-Menten law with respect to the COD of the outlet flow, with a Michaelis constant KCOD of 400mg/L. An inhibition effect occurred above inlet COD of around 3000 mg/L.

Submerged Membrane Bioreactor (SMBR) for Treatment of Textile Dye Wastewatertowards Developing Novel MBR Process

This paper deals with the application of a submerged membrane bioreactor (SMBR) with commercial membrane module and novel MBR modulefor the treatment of model textile dye wastewater (MTDW). For this work, MTDW was developed based on different publications and a pilot-scale automated SMBR unit was applied to carry out the tests with this model wastewater. The system is on the way to be upgraded to attain novel MBR module replacing the applied commercial membrane by novel membrane materials which have been developed by the European Commission funded project “BioNexGen” [1]. The hydraulic volume of the employed SMBR reactor was 57 L. One flat sheet commercial MBR module was submerged in the reactor. The module consisted of 3 sheets, with 25cm×25cm dimensions of each sheet covering total active membrane area of 0.33 m2. To reach the target, different MBR process parameters like COD, BOD, TOC, pH, conductivity, flux, TMP, MLSS, colour contents, air supply, O2 consumption, HRT, SRT, drying residue, nutrients etc. have been investigated. It is reported that under the operating conditions of permeate flux of 4 L/m2h, around 50 mbar of TMP, 12g/L of MLSS, 40-80h of HRT, 1.0 m3/h of air supply to MBR reactor, pH of 8.2±0.2- 10.5±0.2 and temperature of 18±2°C, the COD removal efficiency was around 90% for 2450mg/L inlet COD fed to the membrane bioreactor and Red and Blue colour removal efficiencies were 25-70% and 20-50% respectively. In order to develop novel MBR process, a novel MBR module has already been applied replacing the commercial one and the preliminary results are reported.

Treatment Efficiency of an Anaerobic Baffled Reactor Treating Low Biodegradable and Complex Particulate Wastewater (blackwater) in an ABR Membrane Bioreactor Unit(MBR-ABR)

The provision of water and sanitation to poor communities by 2015 is one of the United Nations targets for this millennium. In South Africa many communities aspire to waterborne sanitation. However, there is a technology gap for decentralized and sustainable waterborne treatment plants capable of treating domestic wastewater. Domestic wastewater is more commonly treated using aerobic processes, anaerobic processes may be more appropriate for decentralized applications since they do not require aeration. The anaerobic baffled reactor (ABR) was investigated by analysing physicochemical and biochemical data from experiments on a laboratory-scale ABR. A pit latrine sludge diluted with tap water was used to feed the ABR. This feed had different biodegradability characteristics compared to domestic wastewater. COD removal ranged from 52 to 80 % depending on the inlet COD. Some COD removal was due to solids retention in compartments, while it was estimated that only 28% of COD removal was due to biological degradation. Soluble extrapolymeric substances (EPS) which are usually a by product of anaerobic degradation were higher in the feed than in the effluent despite the increasing organic loading rates. More than 50 % of soluble extrapolymeric substances from the load remained in the effluent and were the major cause of membrane fouling for membranes. Also, up to 80% removal efficiencies in terms of total COD and solids were recorded with increasing organic loading rates. While these results do not allow the prediction of ABR-MBR performance during the treatment of real wastewater, it was concluded that most solids retention occurred in the feed tank, COD removal occurred as a result of solids retention and digestion, the loading characteristics influenced only COD and conductivity. The relatively low biodegradability of the feedstock indicates that anaerobic digestion is not the most appropriate treatment for VIP sludge.

Tapered anaerobic hybrid reactor – a better option for treating low‐strength wastewaters

Anaerobic biofilm reactors have limitations in treating wastewaters with low organic substrate concentrations (COD value below 1000 mg/L) because the substrate cannot reach the microorganisms present in the interior part of the biogranules. Hence, the performance of these reactors is mainly influenced by the size of the biogranules present within the reactor. An anaerobic hybrid reactor with a tapered configuration has been developed where the self‐immobilized biogranules are kept under completely fluidized condition. The tapered configuration can retain smaller sized biogranules more effectively than a cylindrical configuration for the same hydraulic loading rate. A synthetic effluent containing glucose as the sole carbon source was used to study the performance of this reactor. The reactor could handle an organic loading rate up to 19.1 kgCOD/(m3·d) with a hydraulic retention time (HRT) of 0.63 h, removing around 90% of inlet COD. Even though the strength of the wastewater is low, the resultant organic loading rate is also high because of the high hydraulic loading rate (low HRT). The specific substrate utilization rate study showed that the concentration of methanogenic bacteria within the biogranules increased along the reactor height, whereas the concentration of acidogens decreased. The morphology and hydrodynamic characteristics of the biogranules obtained from the reactor at different heights were also studied. The biogranules obtained from the upper port of the reactor had a lower diameter, lower terminal settling velocity and more cavities than those from the lower port. Biogranules up to the size of 5.2 mm were observed.