Potentiality of municipal sludge for biological gas production at Soba Station South of Khartoum (Sudan)

The present study investigates the influence of individual and combined hydrogen peroxide and thermal pre-treatment of waste activated sludge on anaerobic digestion. For so doing, it employs anaerobic batch reactors in the mesophilic conditions. For comparison, soluble fractions of organic matter, biogas production, biochemical methane potential, removal of chemical oxygen demand (COD), and volatile solids (VS) have been measured during the anaerobic digestion process in systems with and without pre-treatment. Hydrogen peroxide pre-treatment has been tested in two concentrations of 30 g H2O2/kg VS and 60 g H2O2/kg VS and thermal pre-treatment has been performed at two temperatures of 75℃ and 90℃. According to the results, the solubalisation of organic matter considerably improves, when combined hydrogen peroxide and thermal pre-treatment is employed. As a result, in comparison to the control reactor, higher amounts of biogas (71%) and methane (81%) have been produced in the bioreactor, pre-treated with combined hydrogen peroxide (30 g H2O2/kg VS) and heat (90 ℃). In addition, the removal efficiency of COD and VS from the digested sludge has been enhanced in the pre-treated reactors (up to 39% and 92%, respectively) in comparison to the control reactor. The improved methane yield, COD, and VS are of paramount importance, not only because higher amounts of renewable energy are obtained from the anaerobic digestion process, but because sludge transport costs are reduced and the digested sludge obtains a higher potential application to agricultural lands.

Anaerobic digestion is an effective technology for converting organic waste into biogas while reducing environmental pollution. This study investigates the impact of co-digesting waste-activated sludge (WAS) with wheat straw, rice straw, and bokashi on biogas production. Nine anaerobic batch reactors were operated under mesophilic conditions (35 °C), incorporating different proportions of bokashi (1% and 2%) along with rice and wheat straw (4%). The results revealed that reactors supplemented with wheat and rice straw exhibited higher biogas production than the control reactor (sludge only). Wheat straw outperformed rice straw in improving biogas yield, total solids (TS) reduction, total volatile solids (TVS) degradation, and chemical oxygen demand (COD) removal. The addition of bokashi enhanced biogas production, confirming its role in accelerating organic matter breakdown. The maximum biogas yield was observed in the reactor containing sludge co-digested with wheat straw and 2% bokashi, which generated three times more biogas than the control. This reactor also exhibited the highest degradation rates of TS (57.83%), TVS (66.37%), and COD (71.53%). Furthermore, pH remained stable within the optimal range across all reactors, ensuring a balanced digestion process. Statistical analysis revealed significant correlations between organic matter degradation (COD, TS, TVS reduction) and biogas production, demonstrating that effective substrate decomposition improves biogas yield. The recurrent neural network (RNN) model was applied to experimental data to predict biogas production. With an exceptionally low root mean square error (RMSE) of 0.0041, R2 close to 1, and MAE 0.0117, the model exhibited excellent accuracy and reliability in generating precise predictions.

While palm oil mill effluent (POME) from different sources will have varying characteristics due to the different process flows in mills, efficient monitoring and performance evaluation of anaerobic digesters in POME treatment are crucial to ensure stable biogas production with minimal operational problems. Therefore, this study aims to evaluate and compare the performances of in‐ground lagoon anaerobic digesters under mesophilic conditions in four different biogas plants (BGPs A, B, C and D) located in Malaysia with respect to total chemical oxygen demand (COD) removal and total biogas produced. Results show that all BGPs are still functioning well with satisfactory methane yields (.135–.364 Nm3CH4/kgCOD removed) and COD removal efficiencies (67%–85%). ANOVA analysis shows that organic loading rate (OLR), temperature (T) and recirculation ratio (RR) have significant effects on the COD removal and biogas production of all four plants. BGP B has the highest amount of biogas produced (4.12 × 105 Nm3/month) and COD removal rate amongst other BGPs due to its most stable and lowest T (<40°C), high RR, and consistent and high COD load. Conversely, BGP D has the lowest COD removal and biogas production, which are mainly contributed by a high COD inlet (92 000 mg/L) and a high T in the anaerobic digester (48.7°C). Despite having a similar design of an anaerobic digester, this comparative study reveals that different BGPs will have different optimum operating conditions and limitations, depending not only on the operating conditions of the BGP (OLR, T and RR) but also on the raw POME quality stemming from the palm oil milling process. A future study would be focused on the optimisation of four BGPs for maximum biogas removal.

A novel mesophilic anaerobic digestion process with detoxification-treated coconut shell pyroligneous was established, exhibiting an effective advantage in biogas production. The pyroligneous collected contained 166.2gl(-1) acetic acid, indicating great potential for biogas production. Detoxification was an effective way of simultaneously enriching biodegradable ingredients and removing inhibitors (mainly as phenols and organic acids) for digestion process. The digestion process lasted 96h and fermentation characteristics (chemical oxygen demand (COD) removal ratio, volatile fatty acid (VFA) consumptions, pH, total gas, methane yield, and phenol removal efficiency) were measured. The experiments successfully explored the optimum detoxification parameters, oxidized with 10% H2O2 followed by overliming, and demonstrated 89.3% COD removal, 91.4% methane content, 0.305 LCH4/g COD removed CH4 yield, and 88.81% phenol removal ratio. This study provided clues to overcome the negative effects of inhibitors in pyroligneous on biogas production. The findings could contribute to significant process in detoxified pretreatment of pyroligneous and develop an economically feasible technology for treating pyroligneous after producing charcoal.

The biomethane potential (BMP) of five organic sources with different proximal composition have been investigated during anaerobic digestion (AD). The organic sources have been selected among different Ecuadorian biomass residues according to the criteria, that each one has a high content of one parameter of interest. Therefore, the five organic sources are: blackberries as a residue high in sugars, avocado for high content in lipids, soybean representing high protein content, green plantain peel for starch and sugarcane bagasse for high fibre content. The experimental setup was developed in batch reactors at the mesophilicregime (35°C). All experiments are prepared with a reactive mixture composed of inoculum, basal nutritivemedium (BM) and the organic material (OM) diluted in water with approximate 10% total solids. The experiment of each biomass was performed in three sequential times. The feed and the final reactive mixture were analysed according to the following parameters: chemical oxygen demand (COD), total solids (TS), total volatile solids (VS), pH, volatile fatty acids (VFA) and nitrogen (N). The biogas production is measured by the water displacement method, while the methane content was analysed by GC-TCD / FID. The results showed that the first experiment with high protein content showed the highest cumulative biogas production with 2300 mL in 21 days, while the three experiments with high sugar content produced in average the most biogas (23 mL/day). The high fibre experiment presented the highest methane content as well as the lowest concentration of VFA with 2667 ± 103 (mgCH3COOH/L). Since the VFA profiles presented higher values for the different concentrations, which was also related with low final pH values of reactive mixture, the lowest pH value (4.6 ± 0.8) was observed for reactors charged with high sugar content.

For a country like India where energy continues to be precious, with oil prices continuing to rise unlike in the West, anaerobic digestion has far greater relevance than it has to many other regions of the world. The cassava starch production in our country is mainly concentrated in small to medium scale factories, which generates 30,000–40,000 l of effluent per ton of sago produced. The effluent is acidic and highly organic in nature having chemical oxygen demand (COD) of 5,000–7,000 mg l−1 during the season and 1,000–5,000 during the off-season. These effluents pose a serious threat to the environment and quality of life in the rural area. Since the treatment of cassava starch factory effluents through the normal biogas plants with 30–55 days retention period is very costly, attempts have been made to treat them through high-rate hybrid reactor with several hours of retention period. In Random-Packed Anaerobic Filter, the maximum COD reduction was observed (84.4 %) at 10 h hydraulic retention time (HRT). At 4 h HRT only 46.3 % COD was removed. Even though higher COD removal was achieved at 20 h, the better HRT was at 10 h as the difference between the 20 and 10 h HRT in only 0.2 %. In Up-flow Anaerobic Sludge Blanket reactor, the maximum COD removal (90 %) and total solid (TS) removal (82 %) were observed in a HRT of 30 h, whereas low COD (67 %) and TSs (64 %) removal was observed at 5 h HRT. The treatment of sago industry effluent in a hybrid reactor was studied and the HRT employed was 10, 24, 32, and 40 h. The COD removal rates were 86, 93, 94, and 95 %, and the TSs removal was 79, 85, 86, and 89 %. When the results of all these three reactors were compared, the hybrid reactor seems to be better with an optimum HRT range of 10–20 h. Hence, the anaerobic digestion has proved to be an effective method of treating the sago industry wastewater with simultaneous production of energy in the form of methane.

Quinoline is toxic and difficult to degrade biologically; thus, it is a serious threat to the safety of ecosystems. To promote quinoline reduction, zero-valent iron (ZVI) was introduced into an anaerobic digestion (AD) system through batch experiments. The performance of three different types of ZVI (i.e., iron powder, iron scrap and rusty iron scrap) on quinoline degradation, methane production, formation of volatile fatty acids (VFAs) and chemical oxygen demand (COD) removal were investigated systematically. Compared to the AD system alone, quinoline and COD removal as well as the production of methane and acetic acid were effectively enhanced by ZVI, especially rusty iron scrap. The removal efficiencies of quinoline and COD were increased by 28.6% and 19.9%, respectively. The enhanced effects were attributed to the high accumulation of ferrous ions and high pH self-buffering capability, which were established by ZVI addition. Furthermore, high-throughput sequencing analysis indicated that the functional microorganisms in the ZVI-AD system were higher than in the AD system, and the added types of ZVI played important roles in structuring the innate microbial community in waste activated sludge (WAS). Especially, high enrichment of microorganisms capable of degrading quinoline, such as Pseudomonas and Bacillus, in the coupled system was detected.

ABSTRACTIn this study, real-scale wastewater treatment plant (Hurma WWTP) sludge anaerobic digestion process was modeled by Anaerobic Digestion Model (ADM1) with the purpose of generating the data to understand the process better by contributing to the prediction of the process operational conditions and process performance, which will be a base for future anaerobic sludge stabilization process investments.Real-scale anaerobic sludge digestion process data was evaluated in terms of known process and state variables and also process yields. Average VS removal yield, methane production yield, and methane production rate values of the anaerobic sludge digestion unit were calculated as 46.4%, 0.49 m3CH4/kg VSremoved, and 0.33 m3 CH4/m3day, respectively. In this study, ADM1 was intended to predict the behavior of real-scale anaerobic digester processing sewage sludge under dynamic conditions. To estimate the variables of real-scale sludge anaerobic digestion process with high accuracy and to provide high model prediction performance, values of the four parameters (disintegration rate constant, carbohydrate hydrolysis rate constant, protein hydrolysis rate constant, and lipid hydrolysis rate constant) that have strong effects on structured ADM1 were estimated by using the parameter estimation module in Aquasim program and their values were found as 0.101, 10, 10, and 9.99, respectively. When the numbers of kinetic parameters with the processes included in ADM1 along with the dynamic and non-linear structure of the real scale anaerobic digestion were taken into consideration, model simulations were in good agreement with measured results of the biogas flow rate, methane flow rate, pH, total alkalinity, and volatile fatty acids.

The optimisation and wider utilisation of renewable energy technologies is essential for the sake of the global climate and all life on earth. Anaerobic digestion of organic matter is one such technology that has its place as one of the most important methods of waste reduction and sustainable energy generation. Already being utilised in a multitude of contexts worldwide, anaerobic digestion still has vast unrealised potential. A major cause of this is process inhibition, and one of the main groups of chemical inhibitors is heavy metals. However, the literature is currently lacking in breadth and depth of understanding of the role of heavy metals in anaerobic digestion processes. Furthermore, the addition of trace nutrients to reactors in large-scale applications is becoming a more common practise for the purposes of biogas enhancement and improved reactor stability. However, the detailed effects of specific trace elements on different feedstocks and in various applications has not been widely studied. This work investigated the effects of Co, Fe, Hg, W and Zn on anaerobic digestion processes through a series of laboratory experiments. Sewage sludge spiked with these metals was used as the feedstock for 9L continuously-fed anaerobic digesters and biochemical methane potential tests. Spiked heavy metal concentrations were carefully chosen for the purpose of measuring the impact of selected metals on anaerobic processes. Biogas quantity and quality were continuously recorded, as were the reactor parameters, TS%, VS%, pH, acid/alkalinity ratio, VFA and ammonia concentrations, in order to closely monitor metal-effects over time. Reactor stability and biogas production were negatively affected by Hg, Zn and Fe, with Hg exhibiting extremely toxic effects even at low concentrations. Co had both negative and positive effects on anaerobic processes, depending on the spiking concentration. W exhibited biogas promotion effects at concentrations between 0.6-10ppm, and its addition did not negatively affect reactor stability. Recommendations were made for users of anaerobic digestion technologies regarding the potential damage or enhancement effects certain metals would be expected to have on their reactors.

The objective of this study was to evaluate the influence of roughage‐to‐concentrate ratio on quantification and characterization of sheep manure, and to verify whether the addition of crude glycerin improves the efficiency of the anaerobic digestion process. The characterization study was carried out with two treatments (diet 1 with 40% roughage and 60% concentrate and diet 2 with 60% roughage and 40% concentrate) and 12 replicates per treatment. Parameters evaluated were as follows: production of manure, total solids (TS), volatile solids (VS), most probable number (MPN) of total (TC) and thermotolerant coliforms (TTC), chemical oxygen demand (COD), and residue coefficient. The digestion test was performed in batch digesters that were loaded with sheep manure with the doses of crude glycerin: 0, 3, 6, 9, 12, and 15% in the substrate. The process efficiency was measured by the reduction of TS, VS, and COD as well as the production of biogas. No differences were observed for the production of TS and manure among the diets. The contents of VS, COD, and MPN of TC and TTC were greater in manure from animals fed with higher concentrate ratio. Multiple linear models were generated according to the reductions of VS, TS, COD and production and potential of biogas and methane production and hence, both the additions of concentrate in the diet and crude glycerin in the codigestion influenced, in a positive way, the removal organic load in digesters. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1038–1043, 2015

Most researchers analyse and optimise the anaerobic performance based on the data generated from pilot plants and laboratory scaled experiments, but not from the industrial scale biogas plant. Therefore, this study aims to evaluate, compare, and optimise the performances of an In-ground Lagoon Anaerobic Digester under mesophilic conditions in four different biogas plants (BGP A, B, C and D) located in Malaysia, for total chemical oxygen demand (COD) removal and total biogas produced. Organic loading rate (OLR), temperature, recirculation ratio (RR) and plant location are found to have significant effects on COD removal and biogas production. Sensitivity analysis shows that BGP A, B, and C show a similar trend of sensitivity, i.e., OLR > Temperature > RR. Conversely, the temperature has the highest sensitivity contributing to the Chemical Oxygen Demand (COD) removal for plant D. Despite having a similar anaerobic digester design for each biogas plant, the optimum operating parameters of OLR, temperature and recirculation ratio vary from plant to plant. BGP B can achieve the highest COD removal (1.21 X 106 kg CODin/month) as well as biogas production rate (4.12 X 105 Nm3/month), with a corresponding methane yield of 0.28 Nm3 CH4/kg CODremoved when the optimal operating parameters for OLR, temperature and RR are configured at 1.60 kg CODin/m3 day, 37.7 °C and 2.08 respectively. It could be concluded that moderate OLR (<1.6), moderate T (<44 °C), and moderate RR (<2.3) are required to achieve optimum COD removal and biogas production for each biogas plant.

The increasing demand of energy supply requires the development of systems of energy production based on the exploitation of renewable energy sources as an alternative to fossil fuels in common use. Through the process of anaerobic digestion it is possible to convert into biogas agricultural biomass, zootechnical waste, sewage sludge and organic fraction of municipal solid waste. After that it is possible to generate energy from biogas through the process of cogeneration. More recent concerns about global warming have stimulated further anaerobic digestion application and the improvement the processes in order to maximize biogas production, which is a renewable and versatile energy source that can be used for heat and electricity production, and as transportation fuel. It is in the interest of operators of anaerobic digestion plants to maximize methane production whilst concomitantly reducing the chemical oxygen demand of the digested material. The pre-treatment of solid waste is regarded as a prerequisite of the anaerobic digestion process to reduce volume and increase methane yield. The aim of the mechanical treatment is the reduction of the size of the biomass and its degree of crystallization, in order to increase the surface area available to enzymatic hydrolysis. This generates an increase on biogas production and a decrease in the time required for the digestion. In this work the link between mechanical pretreatment and the increase of methane yield of some samples of a dedicated crop (triticale) was discussed.

Role of biochar in promoting methanogenesis during anaerobic processes was investigated in this research. Biochar produced from Himalayan pine needles was used as medium for conductive material mediated interspecies electron transfer (CM-IET) amongst the electron producing microorganisms and electron consuming methanogenic archaea. Three anaerobic continuous stirrer tank reactors (CSTRs) with 0, 5 and 10 g/L pine needle biochar (PNB) were operated at steady state organic loading rate (OLR) of 2.0-2.5 kgCOD/(m3.d). R0 (0 g/L PNB), representing indirect interspecies electron transfer (IIET), failed at an OLR of 2.0 kgCOD/(m3.d) due to the highest volatile fatty acid (VFA) concentration of 6,300 mg/L among the three CSTRs. On the other hand, at an OLR of 2.5 kgCOD/(m3.d), R2 (10 g/L PNB) showed the most superior performance with chemical oxygen demand (COD) removal of 55% and volatile fatty acid (VFA) concentration of 3,500 mg/L, while R1 (5 g/L PNB) recorded COD removal of 45% and VFA concentration of 4,400 mg/L. In comparison, fixed biofilm reactor (FBR) with 80 g/L of PNB as support material operated satisfactorily at OLR of 13.8 kgCOD/(m3.d) with 70% COD removal and VFA concentration of 1,400 mg/L. These investigations confirmed the beneficial role of biochar in anaerobic processes by promoting CM-IET amongst VFA degrading bacteria and methane producing archaea.

La vinaza es un residuo derivado de la producción de alcohol carburante, que posee elevada carga orgánica disuelta (46%), bajo pH que oscila entre 3-5 y alta demanda química de oxigeno (DQO) de 200-300 mgDQO/L, dichas características hacen de la vinaza un potencial contaminante. Hoy en día, se han buscado métodos que contribuyan a un adecuado manejo de este residuo, como su aprovechamiento para generar energía. En esta investigación se determinó el efecto de la concentración de vinaza y el tipo de lodo inoculante sobre la tasa global de producción de biogás, actividad metanogénica y reducción de carga orgánica durante el proceso de digestión anaerobia. Se utilizaron lodos como fuente de inóculo, provenientes de una PTAR, de una laguna de vinaza, y de laguna de oxidación y enfriamiento; la producción de biogás se cuantificó con la técnica de desplazamiento de líquido, se determinó la actividad metanogénica específica (AME), se determinó la tasa de remoción de DQO y sólidos totales y se aislaron microorganismos metanogénicos. Se encontró que la concentración de 90% de vinaza con lodos de la laguna de oxidación obtuvo los mejores rendimientos, se cuantificó 674.5 mL de biogás durante 18 días en un volumen de trabajo de 400 mL y se calculó la AME de 0.2 gDQOCH4/gSSV.d. Se demostró que a partir de la digestión anaerobia reduce un 25.2% de la DQO y 22.4% de sólidos; los resultados del análisis microbiológico permitieron evidenciar la presencia de microorganismos metanogénicos en el biorreactor anaerobio.

Anaerobic digestion of food waste (FW) is typically limited to large reactors due to high hydraulic retention times (HRTs). Technologies such as anaerobic membrane reactors (AnMBRs) can perform anaerobic digestion at lower HRTs while maintaining high chemical oxygen demand (COD) removal efficiencies. This study evaluated the effect of HRT and organic loading rate (OLR) on the stability and performance of a side-stream AnMBR in treating diluted fresh food waste (FW). The reactor was fed with synthetic FW at an influent concentration of 8.24 (± 0.12) g COD/L. The OLR was increased by reducing the HRT from 20 to 1 d. The AnMBR obtained an overall removal efficiency of >97 and >98% of the influent COD and total suspended solids (TSS), respectively, throughout the course of operation. The biological process was able to convert 76% of the influent COD into biogas with 70% methane content, while the cake layer formed on the membrane gave an additional COD removal of 7%. Total ammoniacal nitrogen (TAN) and total nitrogen (TN) concentrations were found to be higher in the bioreactor than in the influent, and average overall removal efficiencies of 17.3 (± 5) and 61.5 (± 3)% of TAN and TN, respectively, were observed with respect to the bioreactor concentrations after 2 weeks. Total phosphorus (TP) had an average removal efficiency of 40.39 (± 5)% with respect to the influent. Membrane fouling was observed when the HRT was decreased from 7 to 5 d and was alleviated through backwashing. This study suggests that the side-stream AnMBR can be used to successfully reduce the typical HRT of wet anaerobic food waste (solids content 7%) digesters from 20 days to 1 day, while maintaining a high COD removal efficiency and biogas production.