Anaerobic Co-digestion Of Sludge Research Articles

Effect of fish waste augmentation on anaerobic co-digestion of sludge with food waste

The effect of sudden augmentation with fish waste (FW) on an operating anaerobic digester was investigated. Fifteen repeated FW spikes (FWS) composed of 1% or 5% FW per working volume of digester were suddenly fed into semi-continuous operation of a mixture of sludge and food waste. Overall process efficiency was not inhibited by FW augmentation. The bacterial community were clustered differently in the 5% FWS treatment than in the control and 1% FWS. Protein-degrading bacteria (Porphyromonadacea, Family XI, and Family XII) were commonly found in the 5% FWS treatment. Their proportions positively correlated with numbers of other bacteria and dominant methanogens (Methanosaeta and Methanospirillum), showing their important role in FWS digestion. FWS caused a shift of bacteria community, but an increase in archaeal concentration. Therefore, sudden addition of an appropriate amount of FW to existing digesters did not provoke process failure. This result contributes an ecologically-benign method to process FW.

Effect of Thermal Pre-treatment and Anaerobic Co-Digestion of Sludge and Waste on Physical Characteristics and Total Organic Carbon Removal

Effect of Thermal Pre-treatment and Anaerobic Co-Digestion of Sludge and Waste on Physical Characteristics and Total Organic Carbon Removal

Anaerobic co-digestion of sludge, sugarcane leaves, and Corchorus stalks in Egypt

Anaerobic co-digestion of sludge, sugarcane leaves, and Corchorus stalks in Egypt

Co-digestion of industrial recycled pulp and paper sludge with vinasse wastewater: experimental and theoretical study

Anaerobic co-digestion of sludge from recycled pulp and paper industry (RPPS) with vinasse effluent from alcohol distilleries (VW) was performed under mesophilic conditions (37 °C) at laboratory scale, using one-liter continuous stirred tank reactors (CSTRs). The physicochemical parameters were monitored during the process. The average pH and alkalinity were 7.7 and 1000 mg CaCO3 Kg−1, respectively, indicating that the process is working well without the risk of acidification. The methane yield and biodegradability of this mixture were determined. The methane yield was about 112 (NmL CH4 g−1 VS added) and biodegradability reached 73%. Nevertheless, in monodigestion of RPPS, the methane yield was 94 (NmL CH4 g−1 VS added) and biodegradability 65%. The anaerobic co-digestion of (RPPS) with (VW) at a proportion of (70:30) improved methane production by 16% and biodegradability by 11%. Bioenergy recovery from industrial (RPPS) is promoted by co-digestion with (VW), and the removal efficiency of 73% indicates the performance of the process adopted. A kinetic study was performed using five models Richards, modified Gompertz, Logistic, Cone, and first order. The results show that Richards' was the most appropriate model for adjusting methane production from (RPPS) and (VW) co-digestion.

The effect of microwave pretreatment on anaerobic co-digestion of sludge and food waste: Performance, kinetics and energy recovery

This paper studied the effect of microwave (MW) pretreatment on anaerobic co-digestion of sludge (SS) and food waste (FW). Using SS and FW as digestive substrates, the MW pretreatment method was used to determine the changes in the substrate matrix by means of batch anaerobic digestion at 37 °C. The kinetics of methane production were calculated, and the changes in organic matter during anaerobic co-digestion, the properties of the anaerobic-digested effluent, and the net energy output of the co-digestion system were determinated. The results showed that MW pretreatment was beneficial to the dissolution of organic matter, conversion of protein to NH4+-N, cumulative methane production, unit biomethane yield, and reaction rate of methane production in the SS and FW anaerobic co-digestion system. The highest cumulative methane production in the co-digestion system reached 3446.3 ± 172.3 mL (35 days), which was 19.93% higher than that of the control. Furthermore, MW pretreatment significantly increased the accumulation of VFAs and the content of butyric acid in the anaerobic-digested effluent, which was beneficial to the methanogenesis process. The MW pretreatment of all co-digested substrates produced a greater net energy output than the control, and the MW-SS + MW-FW group yielded the highest net energy output, which was 76.25 kJ/g Fed VS. The results indicated that MW pretreatment prior to SS and FW anaerobic co-digestion is an effective way to improve the anaerobic digestion efficiency and energy recovery rate.

Methane production from anaerobic co-digestion of sludge with fruit and vegetable wastes: effect of mixing ratio and inoculum type

Methane production from wastes, like sewage sludge and fruit and vegetable wastes, has double benefits; first is minimizing these wastes and second is energy recovery. The goal of this research is to enhance methane yield from anaerobic co-digestion of primary sludge (PS) with fruit and vegetable wastes (FVW) in Egypt using different mixture and various inoculum types. Bio-chemical methane potential (BMP) tests were conducted in a 500-mL glass reactor under mesophilic conditions (35–37 °C). In the first BMP tests, six mixtures with PS to FVW ratios of 100:0, 70:30, 50:50, 30:70, 20:80, and 0:100 (based on volatile solids) were performed to obtain the best mixture for an optimal methane production. In the second BMP tests, three types of inoculum (fresh cow manure, activated sludge, and excess sludge) were used to identify the optimal inoculum for the greatest methane production. The highest methane yield was observed at PS to FVW ratio of 50:50 (141 mL/g VS), which was higher than the individual digestion of the other used feedstock. However, the minimum methane yield was recorded at PS to FVW ratio of 20:80. On the other hand, using the activated sludge as inoculum improved the methane yields from anaerobic co-digestion of PS with FVW compared with the other types of inoculum. Statistical analysis of the results was conducted using ANOVA test. The results conducted that the production of methane was improved by anaerobic co-digestion of PS with FVW and using the activated sludge as inoculum.

Anaerobic Co-Digestion of Sludge and Organic Food Waste—Performance, Inhibition, and Impact on the Microbial Community

Anaerobic co-digestion allows for under-utilised digesters to increase biomethane production. The organic fraction of municipal solid waste (OFMSW), i.e., food waste, is an abundant substrate with high degradability and gas potential. This paper investigates the co-digestion of mixed sludge from wastewater treatment plants and OFMSW, through batch and continuous lab-scale experiments, modelling, and microbial population analysis. The results show a rapid adaptation of the process, and an increase of the biomethane production by 20% to 40%, when co-digesting mixed sludge with OFMSW at a ratio of 1:1, based on the volatile solids (VS) content. The introduction of OFMSW also has an impact on the microbial community. With 50% co-substrate and constant loading conditions (1 kg VS/m3/d) the methanogenic activity increases and adapts towards acetate degradation, while the community in the reference reactor, without a co-substrate, remains unaffected. An elevated load (2 kg VS/m3/d) increases the methanogenic activity in both reactors, but the composition of the methanogenic population remains constant for the reference reactor. The modelling shows that ammonium inhibition increases at elevated organic loads, and that intermittent feeding causes fluctuations in the digester performance, due to varying inhibition. The paper demonstrates how modelling can be used for designing feed strategies and experimental set-ups for anaerobic co-digestion.

Biogas generation related to carbon removal from anaerobic co-digestion of sludge, blood, and swine manure combined in different proportions: Production of biogas by anaerobic co-digestion

This study evaluated, at a laboratory scale, samples composed of wastewater treatment sludge, blood, and swine manure, which were subjected to the process of anaerobic co-digestion. The goal of the study is to identify the reduction of organic loads through the removal of available carbon and its conversion to biogas. The results showed variation in hydraulic retention time, and that the total average volumes of biogas generated in 1-liter (L) reactors filled with 600 milliliters (ml) of samples, ranged from 3.37 to 18.76 L, with percentages of methane ranging between 57.9% and 71.1%. The largest volumes of biogas resulted from blends with lower percentages of swine manure, where the initial amounts of carbon in milligrams per liter (mg/L) were larger within the samples. All of the blends submitted to anaerobic treatment showed reductions in carbon content, and consequently, in chemical and biochemical oxygen demand, demonstrating that the efficiency of biodigesters in the treatment of waste is variable and related to physical–chemical factors, such as the amount of carbon available.

Anaerobic co-digestion of sludge and microalgae grown in municipal wastewater - a feasibility study.

In this study a natural mix of microalgae grown in wastewater of municipal character was co-digested with sewage sludge in mesophilic conditions, in both batch and semi-continuous modes. The semi-continuous experiment was divided into two periods with OLR1 (organic loading rate) of 2.4 kg volatile solids (VS) m-3 d-1 and HRT1 (hydraulic retention time) of 15 days, and OLR2 of 3.5 kg VS m-3 d-1 and HRT2 of 10 days, respectively. Results showed stable conditions during both periods. The methane yield was reduced when adding microalgae (from 200 ± 25 NmL CH4 g VSin-1, to 168 ± 22 NmL CH4 g VSin-1) but VS reduction was also decreased by 51%. This low digestibility was confirmed in the anaerobic batch test. However, adding microalgae improved the dewaterability of the digested sludge. The high heavy metals content in the microalgae resulted in a high heavy metals content in the digestate, making it more difficult to reuse the digestate as fertilizer on arable land. The heavy metals are thought to originate from the flue gas used as a CO2 source during the microalgae cultivation. Therefore the implementation of CO2 mitigation via algal cultivation requires careful consideration regarding the source of the CO2-rich gas.

Energy recovery from fermentative biohydrogen production of biowaste: a case study based analysis

Anaerobic Digestion of biodegradable substrates could be considered a promising process in terms of both bio-fuels and bio-products production. In this respect, biohydrogen production during the acidogenic phase and polyhydroxyalkanoate generation through the metabolites circulation, can be considered the new borders of process optimization. The results of the assessment presented in this work shows that anaerobic co-digestion of sludge and food waste is an effective process to achieve energy self-sufficiency of wastewater treatment plants. Through batch tests it was possible to estimate the production of hydrogen and methane in the specific case of sludge and food waste and calculate the primary energy produced by different users of biogas.

Anaerobic Codigestion of Sludge: Addition of Butcher's Fat Waste as a Cosubstrate for Increasing Biogas Production.

Fat waste discarded from butcheries was used as a cosubstrate in the anaerobic codigestion of sewage sludge (SS). The process was evaluated under mesophilic and thermophilic conditions. The codigestion was successfully attained despite some inhibitory stages initially present that had their origin in the accumulation of volatile fatty acids (VFA) and adsorption of long-chain fatty acids (LCFA). The addition of a fat waste improved digestion stability and increased biogas yields thanks to the higher organic loading rate (OLR) applied to the reactors. However, thermophilic digestion was characterized by an effluent of poor quality and high VFA content. Results from spectroscopic analysis suggested the adsorption of lipid components onto the anaerobic biomass, thus disturbing the complete degradation of substrate during the treatment. The formation of fatty aggregates in the thermophilic reactor prevented process failure by avoiding the exposure of biomass to the toxic effect of high LCFA concentrations.

Co-digestion of used oils and urban landfill leachates with sewage sludge and the effect on the biogas production

This paper evaluates the potential of mesophilic anaerobic digestion (AD) in the treatment of used oils and landfill leachates through co-digestion of the sludge produced in a wastewater treatment plant (WWTP). Biomethane potential (BMP) tests were performed on two different co-substrates and on WWTP sludge. The biogas production per kg of fresh matter of the sludge generated in a WWTP was only 6.1Nl/kg due to its low volatile solids concentration. Biogas production of landfill leachates per kg of fresh matter was found to be low (12.4Nl/kg). The biogas production per kg of fresh matter for the used oil over a period of 47days (not completely degraded) was 970.6Nl/kg. Used oil was selected as co-substrate according to these results. Anaerobic co-digestion of sludge and used oil was conducted in a pilot plant fed in semi-continuous regime in the mesophilic range (38°C) to obtain their adequate mixture in order to ensure the correct function of the process. The optimum oil percentage in the mixture was 19% (volatile solids basis). Once the appropriate mixture was obtained the co-digestion process was carried out in the digester of the Pobla de Farnals WWTP. The co-digestion process improved the performance of volatile matter removal (showing an 11% increase over the period without co-digestion) as well as the biogas production (a 23.5% increase over the period without co-digestion) without disturbing the anaerobic digestion process. The total production of biogas per day in the WWTP increased over the period without co-digestion.

An integrated approach in a municipal WWTP: anaerobic codigestion of sludge with organic waste and nutrient removal from supernatant

Co-digestion appears to be an interesting solution to increase the biogas production of poorly performing under-loaded digesters of waste activated sludge. In the Florence WWTP anaerobic codigestion could increase nitrogen and phosphorus loading rates and thus lower the nutrient removal efficiency. In order to develop an integrated solution to upgrade the Florence WWTP, the different process units were tested in experimental plants. Anaerobic codigestion with source-collected organic solid waste in a pilot-scale bioreactor showed an increase of GPR from 0.15 to 0.45 Nl biogas/l/d with 23% of organic waste loaded. Autotrophic nitrogen removal was carried out in two lab-scale pilot plants which were fed with a real anaerobic supernatant after phosphate removal via struvite formation. The nitritation MBBR has been working for one year at steady-state conditions with a perfect nitrite/ammonium ratio equal to 1:1. Anammox biomass enrichment was performed in a suspended biomass SBR and the specific nitrogen removal rate increased from 1.7 to 58 gN/kgVSS/d in 375 days.

Anaerobic co-digestion of sludge with other organic wastes in small wastewater treatment plants: an economic considerations evaluation

This paper deals with an economic comparison between costs and incomes in small wastewater treatment plants where the anaerobic co-digestion process of sludge and biowaste with energy recovery is operated. Plants in the size range 1,000-30,000 persons equivalent (pe) were considered in the study: typical costs, comprehensive of capital and operating costs, were in the range euro69-105 per person per year depending on the plant size: the smaller the size the higher the specific cost. The incomes deriving from taxes and fees for wastewater treatment are generally in the range euro36-54 per person per year and can only partially cover costs in small wastewater treatment plants. However, the co-treatment of biowaste and the use of produced energy for extra credits (green certificates) determine a clear improvement in the possible revenues from the plant. These were calculated to be euro23-25 per person per year; as a consequence the costs and incomes can be considered comparable for wastewater treatment plants (WWTPs) with size larger than 10,000 pe. Therefore, anaerobic co-digestion of biowaste and sludge can also be considered a sustainable solution for small wastewater treatment plants in rural areas where several different kinds of biowaste are available to enhance biogas production in anaerobic reactors.

Anaerobic co-digestion of sludge with other organic wastes and phosphorus reclamation in wastewater treatment plants for biological nutrients removal

This paper deals with the performances obtained in full scale anaerobic digesters co-digesting waste activated sludge from biological nutrients removal wastewater treatment plants, together with different types of organic wastes (solid and liquid). Results showed that the biogas production can be increased from 4000 to some 18,000 m3 per month when treating some 3-5 tons per day of organic municipal solid waste together with waste activated sludge. On the other hand, the specific biogas production was improved, passing from 0.3 to 0.5 m3 per kgVS fed the reactor, when treating liquid effluents from cheese factories. The addition of the co-substrates gave minimal increases in the organic loading rate while the hydraulic retention time remained constant. Further, the potentiality of the struvite crystallisation process for treating anaerobic supernatant rich in nitrogen and phosphorus was studied: 80% removal of phosphorus was observed in all the tested conditions. In conclusion, a possible layout is proposed for designing or upgrading wastewater treatment plants for biological nutrients removal process.