Volatile Solids Degradation Research Articles

Production of nitrate-rich compost from the solid fraction of dairy manure by a lab-scale composting system

In the present study, we developed an efficient composting process for the solid fraction of dairy manure (SFDM) using lab-scale systems. We first evaluated the factors affecting the SFDM composting process using different thermophilic phase durations (TPD, 6 or 3days) and aeration rates (AR, 0.4 or 0.2 lmin−1kg−1-total solid (TS)). Results indicated that a similar volatile total solid (VTS) degradation efficiency (approximately 60%) was achieved with a TPD of 6 or 3days and an AR of 0.4 l min−1 kg−1-TS (hereafter called higher AR), and a TPD of 3days resulted in less N loss caused by ammonia stripping. N loss was least when AR was decreased to 0.2 l min−1 kg−1-TS (hereafter called lower AR) during the SFDM composting process. However, moisture content (MC) in the composting pile increased at the lower AR because of water production by VTS degradation and less water volatilization. Reduced oxygen availability caused by excess water led to lower VTS degradation efficiency and inhibition of nitrification. Adding sawdust to adjust the C/N ratio and decrease the MC improved nitrification during the composing processes; however, the addition of increasing amounts of sawdust decreased NO3− concentration in matured compost. When an improved composting reactor with a condensate removal and collection system was used for the SFDM composting process, the MC of the composting pile was significantly reduced, and nitrification was detected 10–14days earlier. This was attributed to the activity of ammonia-oxidizing bacteria (AOB). Highly matured compost could be generated within 40–50days. The VTS degradation efficiency reached 62.0% and the final N content, NO3− concentration, and germination index (GI) at the end of the composting process were 3.3%, 15.5×103mg kg−1-TS, and 112.1%, respectively.

Bacterial communities and their association with the bio-drying of sewage sludge

Bio-drying is a technology that aims to remove water from a material using the microbial heat originating from organic matter degradation. However, the evolution of bacterial communities that are associated with the drying process has not been researched systematically. This study was performed to investigate the variations of bacterial communities and the relationships among bacterial communities, water evaporation, water generation, and organic matter degradation during the bio-drying of sewage sludge. High-throughput pyrosequencing was used to analyze the bacterial communities, while water evaporation and water generation were determined based on an in situ water vapor monitoring device. The values of water evaporation, water generation, and volatile solids degradation were 412.9 g kg−1 sewage sludge bio-drying material (SSBM), 65.0 g kg−1 SSBM, and 70.2 g kg−1 SSBM, respectively. Rarefaction curves and diversity indices showed that bacterial diversity plummeted after the temperature of the bio-drying pile dramatically increased on d 2, which coincided with a remarkable increase of water evaporation on d 2. Bacterial diversity increased when the pile cooled. During the thermophilic phase, in which Acinetobacter and Bacillus were the dominant genera, the rates of water evaporation, water generation, and VS degradation peaked. These results implied that the elevated temperature reshaped the bacterial communities, which played a key role in water evaporation, and the high temperature also contributed to the effective elimination of pathogens.

Production of biogas from poultry litter mixed with the co-substrate cow dung

Poultry litter (a mixture of rice hulls, sawdust and chicken excreta of broilers) mixed with the co-substrate cow dung and poultry droppings was evaluated under anaerobic conditions for the production of biogas (methane). Four laboratory scale reactors, R1, R2, R3 and R4, were set up with different proportions of waste poultry litter, cow dung and poultry droppings and had a 6% total solid concentration. Digestion was carried out for 50 days at room temperature, 32±3°C. Volatile solid degradation and specific gas production in the four reactors was 46%, 51.99%, 51.96%, 43% and 0.263, 0.469, 0.419, 0.221l/g, respectively, based on the volatile solid (VS) feed. The methane yields were 71%, 72.5%, 72.6% and 70%, respectively. The COD reductions were 46.1%, 50.76%, 48.23% and 45.12%, respectively. A kinetic analysis showed that the anaerobic digestion of poultry litter with a co-substrate followed first order kinetics. Among the experimental reactors, R2 (25% cow dung, 75% poultry litter) gave the optimum results: a VS reduction of 51.99%, a specific gas yield of 0.469l/g and a methane yield of 72.5%.

Anaerobic digestion of ultrasonicated sludge at different solids concentrations - Computation of mass-energy balance and greenhouse gas emissions

Two cases of anaerobic digestion (AD) of sludge, namely (i) with pre-treatment and (ii) without pre-treatment, were assessed using mass-energy balance and the corresponding greenhouse gas (GHG) emissions. For a digestion period of 30 days, volatile solids degradation of the control sludge and the ultrasonicated secondary sludge was 51.4% and 60.1%, respectively. Mass balance revealed that the quantity of digestate required for dewatering, transport and land application was the lowest (20.2 × 106 g dry sludge/day) for ultrasonicated secondary sludge at 31.4 g TS/L. Furthermore, for ultrasonicated secondary sludge at 31.4 g TS/L, the maximum net energy (energy output − energy input) of total dry solids (TDS) was 7.89 × 10−6 kWh/g and the energy ratio (output/input) was 1.0. GHG emissions were also reduced with an increase in the sludge solids concentration (i.e., 40.0 g TS/L < 30.0 g TS/L < 20.0 g TS/L). Ultrasonication pre-treatment proved to be efficient and beneficial for enhancing anaerobic digestion efficiency of the secondary sludge when compared to the primary and mixed sludge.

Enhancement of aerobic biodegradability potential of municipal waste activated sludge by ultrasonic aided bacterial disintegration

An investigation was performed to study the influence of ultrasonic aided bacterial disintegration on the aerobic degradability of sludge. In first phase of the study, effective floc disruption was achieved at an ultrasonic specific energy input of 2.45kJ/kg TS with 44.5mg/L of Extracellular Polymeric Substance (EPS) release including 0.035U/mL and 0.025U/mL protease and amylase activity respectively. In second phase, experimental outcomes revealed bacterial disintegration of floc disrupted-sludge showing a maximum solubilization of about 23% and was observed to be superior to bacterially disintegrated (11%) and control (6%), respectively. The result of aerobic biodegradability of ultrasonic aided bacterially pretreated sludge showed volatile solids (VS) degradation of about 40.2%. The kinetic study of aerobic biodegradability through non linear regression modelling reveals that floc disrupted sludge showed better biodegradability with decay constant of about 0.19d−1 relatively higher than the control (0.14d−1) and bacterially disintegrated (0.17d−1) sludges.

Characterisation of biogas plants on organic farms and potentials for improvement

Biogas plants on organic farms contribute little to the total installed electrical capacity of biogas in Germany (<1.0 %). To increase the energy efficiency, parameters of biogas plant specifications, fermentation characteristics and feedstock composition were examined for inherent problems in 13 biogas plants. Biogas plants with two reactor stages were found to have significantly higher substrate degradation efficiency and better overall process performance than single-stage biogas plants. The main factor for low volatile solid (VS) degradation was process temperature (range 17 to 49 °C) before hydraulic retention time (HRT) and organic loading rate (OLR). Low VS degradation was found in biogas plants with only one reactor stage, low fermentation temperature and a high share of livestock manure. The total feedstock of the biogas plants comprised mainly of livestock residues (61 %) and grass silage (14 %). The individual biogas plant feedstocks showed strong intake variability and, in general, low specific methane yields (median 256.34 m3 kg−1 VS) when compared to German average. The presented study specified several optimisation pathways for biogas production within the organic farming. Residue storage covers would lessen ecological and economic disadvantages of high VS contents in the effluents considerably. Technical changes in combined heat and power (CHP) units and reactor content recirculation show a way to increase process temperatures and HRT which, in turn, would improve VS degradation efficiency. Moreover, the German Renewable Energies Sources Act 2014 offers possibilities for new small-scaled (≤75 kWel) manure processing (≥80 % fresh weight (FW)) biogas plant installations, an opportunity to increase the total installed electrical capacity of biogas plants on organic farms.

Determination of the archaeal and bacterial communities in two-phase and single-stage anaerobic systems by 454 pyrosequencing

2-Phase anaerobic digestion (AD), where the acidogenic phase was operated at 2day hydraulic retention time (HRT) and the methanogenic phase at 10days HRT, had been evaluated to determine if it could provide higher organic reduction and methane production than the conventional single-stage AD (also operated at 12days HRT). 454 pyrosequencing was performed to determine and compare the microbial communities. The acidogenic reactor of the 2-phase system yielded a unique bacterial community of the lowest richness and diversity, while bacterial profiles of the methanogenic reactor closely followed the single-stage reactor. All reactors were predominated by hydrogenotrophic methanogens, mainly Methanolinea. Unusually, the acidogenic reactor contributed up to 24% of total methane production in the 2-phase system. This could be explained by the presence of Methanosarcina and Methanobrevibacter, and their activities could also help regulate reactor alkalinity during high loading conditions through carbon dioxide production. The enrichment of hydrolytic and acidogenic Porphyromonadaceae, Prevotellaceae, Ruminococcaceae and unclassified Bacteroidetes in the acidogenic reactor would have contributed to the improved sludge volatile solids degradation, and ultimately the overall 2-phase system's performance. Syntrophic acetogenic microorganisms were absent in the acidogenic reactor but present in the downstream methanogenic reactor, indicating the retention of various metabolic pathways also found in a single-stage system. The determination of key microorganisms further expands our understanding of the complex biological functions in AD process.

Assessing the potential of coal ash and bagasse ash as inorganic amendments during composting of municipal solid wastes

This study investigates the potential of incorporating inorganic amendments such as coal and bagasse ashes in different composting mixes. 10 different composting mixes were assessed as follows: A-20% bagasse ash (BA) with unsorted municipal solid wastes (UMSW); B-40% BA with UMSW; C-UMSW; D-20% BA with sorted municipal solid wastes (SMSW); E-40% BA with SMSW; F-SMSW; G-20% coal ash (CA) with UMSW; H-40% CA with UMSW; I-20% CA with SMSW and J-40% CA with SMSW. The composting processes were carried out in rotary drum composters. Composting mixes D, F, G and I achieved a temperature above 55 °C for at least 3 days, with the following peak temperatures: D-62 °C, F-57 °C, G-62 °C and I-58 °C. D resulted in the highest average net Volatile solids (VS) degradation of 68.6% and yielded the highest average volume reduction of 66.0%. The final compost from D, G, I, C and F were within range for electrical conductivities (EC) (794–1770 μS/cm) and pH (6.69–7.12). The ashes also helped in maintaining high average water holding capacities within the range of 183–217%. The C/N ratio of sorted wastes was improved by the addition of 20% coal ash and bagasse ash. Higher germination indices, above 0.8 were obtained for the ash-amended compost (D, G, I), indicating the feasibility and enhancement of using bagasse and coal ash as inorganic amendment in the composting process. Regarding heavy metals content, the chromium concentration for the composting mix G was found to be the highest whereas mixes D and I showed compliance with the MS (Mauritian Standards) 164 standards.

Amount of energy recoverable from an existing sludge digester with the co-digestion with fruit and vegetable waste at reduced retention time

The working operations of a full-scale digester of a wastewater treatment plant for waste-mixed sludge (WMS) stabilization was reproduced using a pilot-scale apparatus. The effect of WMS co-digested with fruit and vegetable waste (FVW) was investigated at different organic loading rates (OLR), from 1.46 kg VS/m3 day to 2.8 kg VS/m3 day, and reduced hydraulic retention time, from 14 days to about 10 days. Methane production per unit of digester volume increased from about 140 NL/m3 day to a maximum value of about 900 NL/m3 day when OLR was increased from 1.46 kg VS/m3 day to 2.1 kg VS/m3 day. Higher OLR caused an excessive HRT reduction, decreasing the percentage of volatile solids degradation without significantly affecting process stability. The maximum electrical energy producible from the full-scale anaerobic facility was about 3,500,000 kW h/year. In these conditions the electrical power output and the net efficiency of the co-generator were 470 kW and 37%, respectively.

Similar PAH fate in anaerobic digesters inoculated with three microbial communities accumulating either volatile fatty acids or methane.

Urban sludge produced on wastewater treatment plants are often contaminated by organic pollutants such as polycyclic aromatic hydrocarbons (PAH). Their removal under methanogenic conditions was already reported, but the factors influencing this removal remain unclear. Here, we determined the influence of microbial communities on PAH removal under controlled physico-chemical conditions. Twelve mesophilic anaerobic digesters were inoculated with three microbial communities extracted from ecosystems with contrasting pollution histories: a PAH contaminated soil, a PCB contaminated sediment and a low contaminated anaerobic sludge. These anaerobic digesters were operated during 100 days in continuous mode. A sterilised activated sludge, spiked with 13 PAH at concentrations usually encountered in full-scale wastewater treatment plants, was used as substrate. The dry matter and volatile solid degradation, the biogas production rate and composition, the volatile fatty acids (VFA) production and the PAH removals were monitored. Bacterial and archaeal communities were compared in abundance (qPCR), in community structure (SSCP fingerprinting) and in dominant microbial species (454-pyrosequencing). The bioreactors inoculated with the community extracted from low contaminated anaerobic sludge showed the greater methane production. The PAH removals ranged from 10 % to 30 %, respectively, for high and low molecular weight PAH, whatever the inoculums tested, and were highly correlated with the dry matter and volatile solid removals. The microbial community structure and diversity differed with the inoculum source; this difference was maintained after the 100 days of digestion. However, the PAH removal was not correlated to these diverse structures and diversities. We hence obtained three functional stable consortia with two contrasted metabolic activities, and three different pictures of microbial diversity, but similar PAH and matter removals. These results confirm that PAH removal depends on the molecule type and on the solid matter removal. But, as PAH elimination is similar whether the solid substrate is degraded into VFA or into methane, it seems that the fermentative communities are responsible for their elimination.

Effect of initial pH on anaerobic co-digestion of kitchen waste and cow manure

This study investigated the effects of different initial pH (6.0, 6.5, 7.0, 7.5 and 8.0) and uncontrolled initial pH (CK) on the lab-scale anaerobic co-digestion of kitchen waste (KW) with cow manure (CM). The variations of pH, alkalinity, volatile fatty acids (VFAs) and total ammonia nitrogen (NH4+–N) were analyzed. The modified Gompertz equation was used for selecting the optimal initial pH through comprehensive evaluation of methane production potential, degradation of volatile solids (VS), and lag-phase time. The results showed that CK and the fermentation with initial pH of 6.0 failed. The pH values of the rest treatments reached 7.7–7.9 with significantly increased methane production. The predicted lag-phase times of treatments with initial pH of 6.5 and 7.5 were 21 and 22days, which were 10days shorter than the treatments with initial pH of 7.0 and 8.0, respectively. The maximum methane production potential (8579mL) and VS degradation rate (179.8mL/g VS) were obtained when the initial pH was 7.5, which is recommended for co-digestion of KW and CM.

Batch and continuous biogas production arising from feed varying in rice straw volumes following pre-treatment with extrusion

This paper studies the synergistic effects on biogas production obtained when different feedstocks are co-digested with varying proportions of rice straw and explores their behavior at the laboratory scale in continuously stirred digesters. Evaluative measures included methane production, volatile solids degradation, ash accumulation, and extrusion effectiveness. The effect of extrusion on the production of energy was also investigated. Results indicated that continuous stirred digesters fed with substrates composed of 10% or 30% of ensiled rice straw (on total FM) produced 146.1 and 140.0lNCH4kgDM−1day−1, respectively. When extrusion was employed, organic matter degradation was promoted and methane production was significantly raised—by as much as 16%. For the feeds containing 10% rice straw, the increase in obtained energy was higher than the energy needed for the extrusion, but the energy balance was close to zero when the percentage of rice straw was the 30% of the feed.

Effect of different livestock dungs as inoculum on food waste anaerobic digestion and its kinetics

The aim of this study was to evaluate the effect of different livestock inoculums on the anaerobic digestion of food waste (FW). Five different livestock dungs i.e., poultry dung (PD), goat dung (GD), cow dung (CD), piggery dung (PGD) and rhinoceros dung (RD) were utilized as inoculums and their effects were valued in various food to microorganism (F/M) ratios in batch reactors. Different livestock dungs achieved higher methane production and volatile solids (VS) reduction in different F/M ratios such as PD, GD, CD, PGD and RD achieved at F/M ratio maintained at 1.5, 2, 2, 1.5 and 1.5, respectively. The results indicated that CD and PGD inoculum were more suitable for the anaerobic digestion of FW than other livestock dungs. Reactors inoculated with CD achieved higher methane production (227mLg−1VS degraded) and volatile solids degradation (54.58%) at F/M ratio maintained at 2.

Fungal Pretreatment of Albizia Chips for Enhanced Biogas Production by Solid-State Anaerobic Digestion

Albizia biomass is a forestry waste that has recently been studied for biogas production by solid-state anaerobic digestion (SS-AD). However, albizia chips showed low methane yields because of their recalcitrant structure. In this study, albizia chips were pretreated by Ceriporiopsis subvermispora, a white-rot fungus, for enhanced biogas production by SS-AD. After 48 days of fungal pretreatment, degradation of lignin in albizia chips was found to be around 24%, which was about 2 times that of cellulose and hemicellulose. Fungal pretreatment of albizia chips resulted in more than 4-fold increases in glucose and xylose yields during 72 h of enzymatic hydrolysis and a 3.7-fold increase in the cumulative methane yield during 58 days of SS-AD. Degradation of volatile solids, cellulose, and hemicellulose in pretreated albizia chips was more than 4 times as high as that in raw albizia chips during SS-AD. These experimental results indicated that fungal pretreatment of albizia chips with C. subvermispora is a hig...

The Effect of Adding Maize Silage as a Co-Substrate for Anaerobic Animal Manure Digestion

The objective of this study is to evaluate anaerobic co-digestion of different animal waste with maize silage. Cattle, broiler, sheep, and goat manure were digested with/without maize silage and chopped grass on mesophilic conditions (37°C) in batch anaerobic reactor for a period of 69 days. Anaerobic digestion may reduce the Volatile Solid (VS) ratio of the solids and VS degradation efficiencies of the reactors were approximately 40–45%. Maximum VS reduction occurred in cattle, goat manure, and maize silage combination about 46.86% but maximum specific methane yield was obtained in cattle manure and maize silage mixture (CM) as 215.2 mL CH4/g VSdegraded. The methane yield increased by adding maize silage compared to not adding an addition maize silage supplement. C/N ratio, carbohydrate and chemical oxygen demand (COD) amounts were decreased in all reactors with a related to total biogas and methane production. Maximum carbohydrate and COD degradation rates were obtained in CM about 63.03%, 53.5% respectively. The result of this study showed, using maize silage in anaerobic co-digestion of animal manure increased total biogas and methane formation and improved digestion behavior for waste utilization.

Using the properties of soil to speed up the start-up process, enhance process stability, and improve the methane content and yield of solid-state anaerobic digestion of alkaline-pretreated poplar processing residues.

BackgroundSolid-state anaerobic digestion (SS-AD) was initially adopted for the treatment of municipal solid waste. Recently, SS-AD has been increasingly applied to treat lignocellulosic biomass, such as agricultural and forestry residues. However, studies on the SS-AD process are few. In this study, the process performance and methane yield from SS-AD of alkaline-pretreated poplar processing residues (PPRs) were investigated using the properties of soil, such as buffering capacity and nutritional requirements.ResultsThe results showed that the lignocellulosic structures of the poplar sample were effectively changed by NaOH pretreatment, as indicated by scanning electron microscopy and Fourier transform infrared spectra analysis. The start-up was markedly hastened, and the process stability was enhanced. After NaOH pretreatment, the maximum methane yield (96.1 L/kg volatile solids (VS)) was obtained under a poplar processing residues-to-soil sample (P-to-S) ratio of 2.5:1, which was 29.9% and 36.1% higher than that of PPRs (74.0 L/kg VS) and that of experiments without NaOH pretreatment (70.6 L/kg VS), respectively. During steady state, the increase in the methane content of the experiment with a P-to-S ratio of 2.5:1 was 4.4 to 50.9% higher than that of the PPRs. Degradation of total solids and volatile solids ranged from 19.3 to 33.0% and from 34.9 to 45.9%, respectively. The maximum reductions of cellulose and hemicellulose were 52.6% and 42.9%, respectively, which were in accordance with the maximal methane yield. T80 for the maximum methane yield for the experiments with NaOH pretreatment was 11.1% shorter than that for the PPRs.ConclusionsPretreatment with NaOH and addition of soil led to a significant improvement in the process performance and the methane yield of SS-AD of PPRs. The changes in lignocellulosic structures induced by NaOH pretreatment led to an increase in methane yield. For the purpose of practical applications, SS-AD with soil addition is a convenient, economical, and practical technique.

Performance and kinetic study of semi-dry thermophilic anaerobic digestion of organic fraction of municipal solid waste

Anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) is promoted as an energy source and waste disposal. In this study semi dry anaerobic digestion of organic solid wastes was conducted for 45days in a lab-scale batch experiment for total solid concentration of 100g/L for investigating the start-up performances under thermophilic condition (50°C). The performance of the reactor was evaluated by measuring the daily biogas production and calculating the degradation of total solids and the total volatile solids. The biogas yield at the end of the digestion was 52.9L/kg VS (volatile solid) for the total solid (TS) concentration of 100g/L. About 66.7% of the volatile solid degradation was obtained during the digestion. A first order model based on the availability of substrate as the limiting factor was used to perform the kinetic studies of batch anaerobic digestion system. The value of reaction rate constant, k, obtained was 0.0249day−1.

Biodrying of sewage sludge: Kinetics of volatile solids degradation under different initial moisture contents and air-flow rates

This study focuses on the kinetics of the biodegradation of volatile solids (VS) of sewage sludge for biodrying under different initial moisture contents (Mc) and air-flow rates (AFR). For the study, a 32 factorial design, whose factors were AFR (1, 2 or 3L/minkgTS) and initial Mc (59%, 68% and 78% w.b.), was used. Using seven kinetic models and a nonlinear regression method, kinetic parameters were estimated and the models were analyzed with two statistical indicators. Initial Mc of around 68% increases the temperature matrix and VS consumption, with higher moisture removal at lower initial Mc values. Lower AFRs gave higher matrix temperatures and VS consumption, while higher AFRs increased water removal. The kinetic models proposed successfully simulate VS biodegradation, with root mean square error (RMSE) between 0.007929 and 0.02744, and they can be used as a tool for satisfactory prediction of VS in biodrying

Responses of microbial community and acidogenic intermediates to different water regimes in a hybrid solid anaerobic digestion system treating food waste

This study investigated the effects of different water regimes in an acidogenic leach bed reactor (LBR) during 16-day batch mode food waste digestion. LBRs were operated under five water replacement ratios (WRRs) (100%, 75%, 50%, 25% and 5% in LBRs R1, R2, R3, R4 and R5, respectively) and methanogenic effluent (ME) addition with two leachate recirculation frequencies (once in 24h and 12h in LBRs R6 and R7, respectively). Results showed that 50–100% WRRs accelerated the hydrolysis and acidogenesis with butyrate as the dominant product (∼35% of COD); whereas 5–25% WRRs promoted propionate production. The ME recirculation enhanced protein decomposition and reduced ethanol production. Lactobacillus dominated in LBRs with water addition (R1–R5), while Clostridium and hetero-fermenting lactic acid bacteria dominated in LBR with ME addition (R7). The highest volatile solid degradation (82.9%) and methane yield (0.29L-CH4/g VS) were obtained with ME addition at 0.7d hydraulic retention time.

Influence of distiller's grains and condensed tannins in the diet of feedlot cattle on biohydrogen production from cattle manure

Biohydrogen production from the manure of cattle fed diets containing corn dried distiller's grains with solubles (DDGS) diets was assessed. Four types of manure were obtained from cattle fed four diets (DDG, %of dietary dry matter): 0 (CK), 20 (DG20), 40 (DG40) and 40 plus 2.5% of dietary dry matter as condensed tannins (DG40CT) and evaluated for biohydrogen production using dark fermentation. Each treatment was evaluated in quadruplicate using 2 L continuously stirred biodigesters operating at 55 °C in batch culture with an organic loading rate of 20 g L−1 volatile solids and a total operation time of 4 d. Gas samples were taken daily to determine hydrogen production, and slurry samples were analyzed daily for volatile fatty acid concentration, total ammonia nitrogen, volatile solids degradation, and soluble ion concentration. The DG0 and DG40 treatments demonstrated the greatest hydrogen production, with DG40CT producing the least (P < 0.001). The inclusion of tannins in the diet of cattle had a negative effect on biohydrogen production from cattle manure, and thus the economic feasibility of using manure as a substrate in anaerobic digestion could be negatively impacted by the inclusion of tannins in the diet.