Treatment of septic tank effluent using moving-bed biological reactor: kinetic and biofilm morphology

Septic tanks are very commonly used wastewater collection systems throughout the world, and especially in rural areas. In this study, the use of moving-bed biological reactors (MBBR) for the treatment of septic tank effluent (STE) was examined. The study was conducted in two phases. In Phase I, the performance of septic tanks from four projects working under different operational conditions and with different service lives was followed to determine the parameters that required further treatment. In Phase II, four specially designed continuous flow pilot-plant MBBRs and one laboratory-scale batch reactor were tested for their efficiency in treating STE. Experiments were carried out at various temperatures (8–25 °C) and with different hydraulic retention times (HRTs). MBBR effectively reduced STE’s nutrients and chemical oxygen demand by 90 and 85 %, respectively, over 180 days of operation. The average ammonia removal rate at 25 °C increased from 0.279 to 0.540 kg N/m3 when the reactor HRT changed from 5.7 to 13.3 h. Under these conditions, the ammonia removal kinetics were successfully correlated with a theta model with an average θ value of 1.054. The biofilm morphology showed a stable and global biomass coverage (>70 %) and a high percentage of live cells. A thinner biofilm was observed when the MBBR operated at high temperatures. The results of this study showed that MBBR is a promising technology for post-treatment of septic tank effluent.Scopu

Enhancement of biogas production from agricultural wastes via pre-treatment with advanced oxidation processes

The effects of advanced oxidation processes (AOPs) including Fenton, ozone, and ozone combined with Fe(II) and H2O2 on disintegration/solubilization of three mixed agricultural solid wastes and subsequent anaerobic digestion were studied. Hydroxyl radicals (̇OH) generated from AOPs enhanced the oxidation of COD and solubilization of particulate COD (>0.45 µm). Upon treatment, substrates lost 15.2 to 29.5% of their solids, 33.6 to 37.5% of total chemical oxygen demand, 16.5 to 25% of total biopolymers (humic acids and protein). The soluble matter content increased by 3–6 folds facilitating metabolization rate of the treated substrate resulting in a 23–30% increase in the cumulative methane production and 11.2–25% increase in % digestion efficiency (%ηAD). Semi-batch tests revealed that mixing fresh and pre-treated substrate using a 50:50 ratio improved both the specific methane production (1.7 folds) and volatile sold reduction (79%) with a positive effect on sludge dewaterability.Scopu

Intermediate ozonation to enhance biogas production in batch and continuous systems using animal dung and agricultural waste

Agricultural waste and animal manure (dung) pose an environmental threat in developing countries. This investigation focused on the possible use of such waste as an energy source in the form of biogas produced via anaerobic digestion (AD). The impact of single and mixed substrates on methane production under controlled batch and continuous experimental setups was considered. The study was extended to investigate the effect of substrate size and the impact of an intermediate ozonation process on enhancing the production of biogas from single and mixed substrates. Cumulative methane production (CMP), ultimate methane yield (UMY), methane production potential (MPP), methane production rate (MPR), and maximum methane production rate (MPRmax) were used as performance indicators of the effectiveness of the anaerobic digestion process. CMP and MPP from mixed substrates were found to be higher than values obtained from a single substrate feeds, which may be attributed to a more balanced nutrient and organic matter found in mixed substrates. The large surface area of fine substrate influenced MPR and MPRmax values in the first 30 days of digestion. In later AD stages, the effect of substrate size was negligible. The MPRmax for fine substrates was 12.3 ± 0.3 LkgVS−1 compared to 8.8 ± 0.2 LkgVS−1 obtained for coarse substrate. Continuous AD with organic loading rate (OLR) of 4 kgVSm−1d−1 showed a %ADefficiency of 62%, an average specific methane production in the range of 98–230 LkgVS−1 and a volumetric methane production rate in the range of 1.94–2.35 m3 m−3d−1. Increasing the OLR increased the accumulation of volatile fatty acids in the system and resulted in decreased methane production. Two-stage AD with an intermediate ozonation process showed a significant increase in CMP and %ADefficiency compared with single-stage AD. The %ADefficiency for two-stage AD ranged from 63% to 83%, and for single-stage AD, it was in the range of 42.2%–64.3%. Anaerobic digestion of mixed agricultural waste improved the filtration, dewaterability, and settling ability of the final substrate, making it suitable for use as a soil fertilizer.The author greatly acknowledges the financial supports provided by Jordanian ministry of higher education (Project 2008/1634/2-H) and Qatar National Research Fund (NPRP No.: 6-1436-2-581). The authors gratefully acknowledge the support provided by the Qatar University to do this work.Scopu

Improving biogas production from agricultural waste by photo-Fenton process

The Study investigates the enhancement of biogas production from a mixture of agricultural solid waste, wastewater and manure by Photo-Fenton prices process. The effect of the total solids, organic content, nutrient and the structure of the substrate on the production of the biogas were assisted. The performance of anaerobic digestion (AD) was monitored by following volatile solids removal efficiencies, biogas production rate and biogas yield ands composition. A number of strategies including controlling the composition of the substrate and employing chemical oxidation process where tested to determine if they resulted in an increase in that in amount of biogas production. The cumulative biogas production for 30 h of digestion ranged from 16.2 to 69.8L/kgVS.h, with the highest production rate for substrate with C/NL ratios in the range 20-30., COD in the range 185 to 40 mg/L an TS in the range 100-15%. The production of by biogas increased by increasing substrate VS/TS ratio, reaching a cumulative biogas production rate of 29.8 NL as a VS/TS ratio of 45%, and a 60,5 NL at a VS/TS ratio of 76. Using photo thing as an intermediate oxidation process between two Ads improved biogas production by 19 to 31.3% for the same substrate.Scopu