Mesophilic and thermophilic anaerobic co-digestion of abattoir wastewater and fruit and vegetable waste in anaerobic sequencing batch reactors

Anaerobic co-digestion of fruit and vegetable waste (FVW) and abattoir wastewater (AW) was investigated using anaerobic sequencing batch reactors (ASBRs). The effects of hydraulic retention time (HRT) and temperature variations on digesters performances were examined. At both 20 and 10 days biogas production for co-digestion was greater thanks to the improved balance of nutrients. The high specific gas productions for the different digestion processes were 0.56, 0.61 and 0.85 l g⁻¹ total volatile solids (TVS) removal for digesters treating AW, FVW and AW + FVW, respectively. At an HRT of 20 days, biogas production rates from thermophilic digesters were higher on average than from mesophilic AW, FVW and AW + FVW digestion by 28.5, 44.5 and 25%, respectively. However, at 10 days of HRT results showed a decrease of biogas production rate for AW and AW + FVW digestion processes due to the high amount of free ammonia at high organic loading rate (OLR).     

Potential for methane production from anaerobic co-digestion of swine manure with winery wastewater

This work examines the methane production potential for the anaerobic co-digestion of swine manure (SM) with winery wastewater (WW). Batch and semi-continuous experiments were carried out under mesophilic conditions. Batch experiments revealed that the highest specific methane yield was 348 mL CH₄ g⁻¹ COD added, obtained at 85.4% of WW and 0.7 g COD g⁻¹ VS. Specific methane yield from SM alone was 27 mL CH₄ g⁻¹ COD added d⁻¹. Furthermore, specific methane yields were 49, 87 and 107 mL CH₄ g⁻¹ COD added d⁻¹ for the reactors co-digesting mixtures with 10% WW, 25% WW and 40% WW, respectively. Co-digestion with 40% WW improved the removal efficiencies up to 52% (TCOD), 132% (SCOD) and 61% (VSS) compared to SM alone. These results suggest that methane can be produced very efficiently by the co-digestion of swine manure with winery wastewater.     

Biomass adaptation over anaerobic co-digestion of sewage sludge and trapped grease waste

The feasibility of sewage sludge co-digestion using intermediate waste generated inside a wastewater treatment plant, i.e. trapped grease waste from the dissolved air flotation unit, has been assessed in a continuous stirred lab reactor operating at 35 °C with a hydraulic retention time of 20 days. Three different periods of co-digestion were carried out as the grease waste dose was increased. When the grease waste addition was 23% of the volatile solids fed (organic loading rate 3.0 kg_COD m⁻³ d⁻¹), an increase in methane yield of 138% was reported. Specific activity tests suggested that anaerobic biomass had adapted to the co-substrate. The adapted inoculum showed higher acetoclastic methanogenic and β-oxidation synthrophic acetogenic activities but lower hydrogenotrophic methanogenic activity. The results indicate that a slow increase in the grease waste dose could be a strategy that favours biomass acclimation to fat-rich co-substrate, increases long chain fatty acid degradation and reduces the latter’s inhibitory effect.     

Pretreatment of pulp mill secondary sludge for high-rate anaerobic conversion to biogas

Three pretreatment methods were compared based on their ability to increase the extent and rate of anaerobic bioconversion of pulp mill secondary sludge to biogas. The pretreatment technologies used in these experiments were: (i) thermal pretreatment performed at 170 °C; (ii) thermochemical (caustic) pretreatment performed at pH 12 and 140 °C; and (iii) sonication performed at 20 kHz and 1 W mL⁻¹. Sludge samples were obtained from a sulfite and a kraft pulp mill, and biochemical methane potential (BMP) assays were performed using microbial granules obtained from a high-rate anaerobic digester operating at a pulp mill. Biogas production from untreated sludge was 0.05 mL mg⁻¹ of measured chemical oxygen demand (COD) and 0.20 mL mg⁻¹ COD for kraft and sulfite sludge, respectively. Thermal pretreatment had the highest impact on sludge biodegradability. In this case, biogas yield and production rate from sulfite sludge increased by 50% and 10 times, respectively, while biogas yield and production rate from kraft sludge increased by 280% and 300 times, respectively. Biogas yield correlated to soluble carbohydrate content better than soluble COD.     

A comparison study on the high-rate co-digestion of sewage sludge and food waste using a temperature-phased anaerobic sequencing batch reactor system

Assessing contemporary anaerobic biotechnologies requires proofs on reliable performance in terms of renewable bioenergy recovery such as methane (CH₄) production rate, CH₄ yield while removing volatile solid (VS) effectively. This study, therefore, aims to evaluate temperature-phased anaerobic sequencing batch reactor (TPASBR) system that is a promising approach for the sustainable treatment of organic fraction of municipal solid wastes (OFMSW). TPASBR system is compared with a conventional system, mesophilic two-stage anaerobic sequencing batch reactor system, which differs in operating temperature of 1st-stage. Results demonstrate that TPASBR system can obtain 44% VS removal from co-substrate of sewage sludge and food waste while producing 1.2 m³CH₄/m³_system/d (0.2 m³CH₄/kgVS_added) at organic loading rate of 6.1 gVS/L/d through the synergy of sequencing-batch operation, co-digestion, and temperature-phasing. Consequently, the rapid and balanced anaerobic metabolism at thermophilic stage makes TPASBR system to afford high organic loading rate showing superior performance on OFMSW stabilization.     

Evaluating and modeling biogas production from municipal fat, oil, and grease and synthetic kitchen waste in anaerobic co-digestions

The feasibility of using synthetic kitchen waste (KW) and fat, oil, and grease (FOG) as co-substrates in the anaerobic digestion of waste activated sludge (WAS) was investigated using two series of biochemical methane potential (BMP) tests. Ranges of ideal substrate to inoculum (S/I) ratio were determined for the FOG (0.25-0.75) and KW (0.80-1.26) as single substrates in the first experiment. The second experiment, which estimated the methane production performances of FOG and KW as co-substrates for WAS co-digestion, was conducted based on the optimal parameters selected from the results of the first experiment. Results indicated that co-digestions with FOG and KW enhanced methane production from 117±2.02 mL/gTVS (with only WAS) to 418±13.7 mL/gTVS and 324±4.11 mL/gTVS, respectively. FOG exhibited more biogas production than KW as co-substrate. Non-linear regression results showed that co-substrate addition shortened the lag phases of organic biodegradation from 81.8 (with only WAS) to 28.3 h with FOG and 3.90 h with KW.     

Abundance and distribution of anaerobic protozoa and their contribution to methane production in Lake Cadagno (Switzerland)

Abstract In the uupermost layers of the anoxic sediment in Lake Cadagno, 9 different species of anaerobic protozoa were identified. The total number of these organisms was about 580 cells·ml⁻¹ sediment. Most pf these protozoa contained endosymbiotic methanogenic bacteria which in total amounted to 10⁶ methanogens·ml⁻¹ sediment. In addition to the methanogenic endosymbionts, cells of Metopus setosus and Caenomorpha lata also contained a non-fluorescent bacterial rod inside the cytoplasm. In some individual cells of C. lata this second type of endosymbiotic bacterium was sometimes the only endosymbiont observed. Contrary to earlier suggestions, anaerobic protozoa do not seem to play a major role in methane production at least in Lake Cadagno. No significant methane production due to the anaerobic protozoa and their methanogenic endosymbionts was found in situ. Isolated ciliates and amoebae produced methane at 12°C, but not at 6°C, probably as a result of temperature limitation. In the sediment of Lake Cadagno sulfate reduction seemed to be the dominant terminal degradation process.     

Efficient production of cellulase in the culture of Acremonium cellulolyticus using untreated waste paper sludge

Cellulase was produced by Acremonium cellulolyticus using untreated waste paper sludge (PS) as the carbon source. The clay present in PS did not show any inhibitory effect on cellulase production but did alter the pH during fermentation. On the flask scale, the maleate buffer concentration and pH were key factors that affected the efficiency of cellulase production from PS cellulose. Optimum cellulase production in a 3-L fermentor of working volume 1.5 L was achieved by controlling the pH value at 6.0 using 2 M NaOH and 2 M maleic acid, and the productivity reached 8.18 FPU/mL. When 40.89 g/L PS cellulose, 2.2 g/L (NH(4) )(2) SO(4) , and 4.4 g/L urea were added to a 48-h culture, the cellulase activity was 9.31 FPU/mL at the flask scale and 10.96 FPU/mL in the 3-L fermentor. These values are ～80% of those obtained when pure cellulose is used as the carbon source. The method developed here presents a new route for the utilization of PS.     

Eliminating methanogenic activity in hydrogen reactor to improve biogas production in a two-stage anaerobic digestion process co-digesting municipal food waste and sewage sludge

Laboratory scale two-stage anaerobic digestion process model was operated for 280 days to investigate the feasibility to produce both hydrogen and methane from a mixture feedstock (1:1 (v/v)) of municipal food waste and sewage sludge. The maximum hydrogen and methane yields obtained in the two stages were 0.93 and 9.5 mL/mL feedstock. To eliminate methanogenic activity and obtain substantial hydrogen production in the hydrogen reactor, both feedstock and mixed liquor required treatment. The heat treatment (100 °C, 10 min) for feedstock and a periodical treatment (every 2-5 weeks, either heating, removal of biomass particles or flushing with air) for mixed liquor were effective in different extent. The methane production in the second stage was significantly improved by the hydrogen production in the first stage. The maximum methane production obtained in the period of high hydrogen production was more than 2-fold of that observed in the low hydrogen production period.     

Development of a pilot scale anaerobic digester for biogas production from cow manure and whey mix

This paper presents results from anaerobic digestion of cow manure and whey mix. A pilot scale anaerobic digester, 128 l in volume, has been developed, to operate under batch and fed-batch conditions. The versatile and unique characteristics of the instrument allowed testing the methane production directly in the farm. The digester performance was evaluated with two calibration tests, the main for a period of 56 days. The study test was divided into three phases, one for each type of feeding operation (batch, fed-batch, batch). The initial phase of digestion resulted in 57 l-CH₄/kg-VS, the second phase had a yield of 86.6 l-CH₄/kg-VS and the third one had a production of 67 l-CH₄/kg-VS. The total methane yield was equal to 211.4 l-CH₄/kg-VS. Using the obtained pilot plant results to a real scale diary production cycle, it was possible to evaluate an electricity production equal to 8.86 kwh per 1 t/d. The conducted tests did show that there is a good potential to the use of a cow manure and whey biomass mix for biogas production.     

Effects of metal oxide nanoparticles (TiO2, Al2O3, SiO2 and ZnO) on waste activated sludge anaerobic digestion

The effect of metal oxide nanoparticles (nano-TiO2, nano-Al2O3, nano-SiO2 and nano-ZnO) on anaerobic digestion was investigated by fermentation experiments using waste activated sludge as the substrates. Nano-TiO2, nano-Al2O3 and nano-SiO2 in doses up to 150 milligram per gram total suspended solids (mg/g-TSS) showed no inhibitory effect, whereas nano-ZnO showed inhibitory effect with its dosages increased. The methane generation was the same as that in the control when in the presence of 6 mg/g-TSS of nano-ZnO, however, which decreased respectively to 77.2% and 18.9% of the control at 30 and 150 mg/g-TSS. The released Zn2+ from nano-ZnO was an important reason for its inhibitory effect on methane generation. It was found that higher dosages of nano-ZnO inhibited the steps of sludge hydrolysis, acidification and methanation. Also, the activities of protease, acetate kinase (AK) and coenzyme F420 were inhibited by higher dosages of nano-ZnO during WAS anaerobic digestion.     

Pretreatment of municipal waste activated sludge for volatile sulfur compounds control in anaerobic digestion

The effect of combination of mechanical and chemical pretreatment of municipal waste activated sludge (WAS) prior to anaerobic digestion was studied using a laboratory scale system with an objective to decrease volatile sulfur compounds in biogas and digested sludge. Mechanical pretreatment was conducted using depressurization of WAS through a valve from a batch pretreatment reactor pressurized at 75 ± 1 psi, while combined pretreatments were conducted using six different dosages of hydrogen peroxide (H₂O₂) and ferrous chloride (FeCl₂) along with mechanical pretreatment. About 37-46% removal of H₂S in biogas occurred for different combined pretreatment conditions. Sludge solubilization achieved due to the mechanical pretreatment increased total cumulative methane production by 8-10% after 30 days during the biochemical methane potential (BMP) test. The pretreatment also improved dewaterability in terms of time to filter (TTF), and decreased methyl mercaptan generation potential of the digested sludge.     

Robustness of archaeal populations in anaerobic co-digestion of dairy and poultry wastes

The objective of this study is to investigate the responses of methanogen populations to poultry waste addition by comparing the archaeal microbial populations in continuous anaerobic digesters with or without the addition of poultry waste as a co-substrate. Poultry waste was characterized as an organic/nitrogen-rich substrate for anaerobic digestion. Supplementing dilute dairy waste with poultry waste for anaerobic co-digestion to increase organic loading rate by 50% resulted in improved biogas production. Elevated ammonia derived from poultry waste did not lead to process inhibition at the organic loadings tested, demonstrating the feasibility of the anaerobic co-digestion of dairy and poultry wastes for improved treatment efficiency. The stability of the anaerobic co-digestion process was linked to the robust archaeal microbial community, which remained mostly unchanged in community structure following increases in organic loading and ammonia levels. Surprisingly, Crenarchaeota archaeal populations, instead of the Euryarchaeota methanogens, dominated the archaeal communities in the anaerobic digesters. The ecological functions of these abundant non-methanogen archaeal populations in anaerobic digestion remain to be identified.     

Co-digestion of intermediate landfill leachate and sewage sludge as a method of leachate utilization

This study examines the co-digestion of intermediate landfill leachate and sewage sludge from a municipal wastewater treatment plant. Application of leachate as a co-fermentation component increased the concentrations of soluble organic compounds (expressed as total organic carbon), ammonium nitrogen, and alkalinity in the digester influents.The biogas yield obtained from the co-fermentation of a 20:1 sewage sludge: intermediate leachate mixture was 1.30 m³ per kg of removed volatile solids (VS), while that from a 10:1 mixture was 1.24 m³ per kg of removed VS. These values exceeded the biogas yield for the sludge alone by 13% and 8%, respectively. The leachate addition influenced the proportion of methane to a minor extent. Increased methane yields of 16.9% and 6.2% per kg of removed VS were found for the two sewage sluge:intermediate leachate mixtures, respectively.     

Evaluation of pretreatment methods on mixed inoculum for both batch and continuous thermophilic biohydrogen production from cassava stillage

Anaerobic sludges, pretreated by chloroform, base, acid, heat and loading-shock, as well as untreated sludge were evaluated for their thermophilic fermentative hydrogen-producing characters from cassava stillage in both batch and continuous experiments. Results showed that the highest hydrogen production was obtained by untreated sludge and there were significant differences (p < 0.05) in hydrogen yields (varied from 32.9 to 65.3 mlH₂/gVS) among the tested pretreatment methods in batch experiments. However, the differences in hydrogen yields disappeared in continuous experiments, which indicated the pretreatment methods had only short-term effects on the hydrogen production. Further study showed that alkalinity was a crucial parameter influencing the fermentation process. When the influent was adjusted to pH 6 by NaHCO₃ instead of NaOH, the hydrogen yield increased from about 40 to 52 mlH₂/gVS in all the experiments. Therefore, pretreatment of anaerobic sludge is unnecessary for practical thermophilic fermentative hydrogen production from cassava stillage.     

Physiological characteristics of cyanobacteria in pulp and paper waste-treatment systems

An investigation was made into the physiological characteristics of the extensive cyanobacterial communities in pulp and paper secondary waste-treatment systems, including the capacity of isolates to biodegrade organic contaminants in these systems. Although pulp and paper waste-treatment systems were found to be severely light-limited, photosynthesis-irradiance curves indicated that shade-adapted cyanobacterial communities could fix conspicuous amounts of inorganic carbon via photosynthesis. Of 21 cyanobacterial strains isolated from pulp and paper waste-treatment systems located in 4 countries, all except one were capable of glucose uptake in the light, and 19 also showed uptake in the dark. In the 6 species tested, glucose and acetate addition stimulated growth in low light in all except one species. Aphanocapsa rivularis grew equally well on glucose and acetate in the dark but Pseudanabaena sp. grew well on acetate, and minimally on glucose. Growth stimulation by glucose and acetate in these two strains was greater in low than in high light. Pseudanabaena sp. and Phormidium animale both accumulated 2,4-dichlorophenol and 3-chlorobenzoate but showed minimal mineralization to CO₂. None of the four species tested could accumulate or degrade phenol or dichloroacetate. It is concluded that, depending on the light conditions, cyanobacteria contribute organic carbon in photosynthesis, and/or remove small organic molecules during mixotrophic and heterotrophic growth but are not important degraders of contaminants in these waste treatment systems.     

Influence of surfactants on anaerobic digestion of waste activated sludge: acid and methane production and pollution removal

The objective of this study is to summarize the effects of surfactants on anaerobic digestion (AD) of waste activated sludge (WAS). The increasing amount of WAS has caused serious environmental problems. Anaerobic digestion, as the main treatment for WAS containing three stages (i.e. hydrolysis, acidogenesis, and methanogenesis), has been widely investigated. Surfactant addition has been demonstrated to improve the efficiency of AD. Surfactant, as an amphipathic substance, can enhance the efficiency of hydrolysis by separating large sludge and releasing the encapsulated hydrolase, providing more substance for subsequent acidogenesis. Afterwards, the short chain fatty acids (SCFAs), as the major product, have been produced. Previous investigations revealed that surfactant could affect the transformation of SCFA. They changed the types of acidification products by promoting changes in microbial activity and in the ratio of carbon to nitrogen (C/N), especially the ratio of acetic and propionic acid, which were applied for either the removal of nutrient or the production of polyhydroxyalkanoate (PHA). In addition, the activity of microorganisms can be affected by surfactant, which mainly leads to the activity changes of methanogens. Besides, the solubilization of surfactant will promote the solubility of contaminants in sludge, such as organic contaminants and heavy metals, by increasing the bioavailability or desorbing of the sludge.     

Hydrogen-producing capability of anaerobic activated sludge in three types of fermentations in a continuous stirred-tank reactor

A continuous stirred-tank reactor was used as an anaerobic sludge system and the hydrogen production capabilities of three typical fermentations, in terms of specific hydrogen production rates, were investigated under the same hydraulic retention times (8 h) and influent chemical oxygen demand (5000 mg/L) at 35 °C. The reactor was continuously fed with diluted molasses, while the pH and oxidation reduction potential in the reactor were regulated to control the type of fermentation. The specific hydrogen production rate of the anaerobic sludge reached 2.96 mol/kg mixed liquid volatile suspended solid (MLVSS)/day, (mol•kg MLVSS^− 1 d^− 1), in ethanol-type fermentation, while 0.57 mol·kg MLVSS^− 1 d^− 1 in butyric acid-type fermentation, and 0.022 mol·kgMLVSS^− 1 d^− 1 in propionic acid-type fermentation. The hydrogen production capability of ethanol-type fermentation was 4.11 times greater than that of butyric acid-type fermentation and 148 times that of propionic acid-type fermentation.     

Biogas production from potato-juice, a by-product from potato-starch processing, in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors

In this study, the utilization of potato-juice, the organic by-product from potato-starch processing, for biogas production was investigated in batch assay and in high rate anaerobic reactors. The maximum methane potential of the potato-juice determined by batch assay was 470 mL-CH₄/gVS-added. Anaerobic digestion of potato-juice in an EGSB reactor could obtain a methane yield of 380 mL-CH₄/gVS-added at the organic loading rate of 3.2 gCOD/(L-reactor.d). In a UASB reactor, higher organic loading rate of 5.1 gCOD/(L-reactor.d) could be tolerated, however, it resulted in a lower methane yield of 240 mL-CH₄/gVS-added. The treatment of reactor effluent was also investigated. By acidification with sulfuric acid to pH lower than 5, almost 100% of the ammonia content in the effluent could be retained during the successive up-concentration process step. The reactor effluent could be up-concentrated by evaporation to minimize its volume, and later be utilized as fertilizer.     

Biodegradation of kraft-lignin by <Emphasis Type="Italic">Bacillus</Emphasis> sp. isolated from sludge of pulp and paper mill

Eight bacterial strains were isolated on kraft lignin (KL) containing mineral salt medium (L-MSM) agar with glucose and peptone from the sludge of pulp and paper mill. Out of these, ITRC-S8 was selected for KL degradation, because of its fast growth at highest tested KL concentration and use of various lignin-related low molecular weight aromatic compounds (LMWACs) as sole source of carbon and energy. The bacterium was identified by biochemical tests as Gram-positive, rod-shaped and non-motile. Subsequent 16S rRNA gene sequencing showed 95% base sequence homology and it was identified as Bacillus sp. In batch experiments, a decrease in pH was observed initially followed by an increase till it reached an alkaline pH, which did not alter the culture growth significantly. The bacterium reduced the colour and KL content of 500 mg l⁻¹ KL in MSM, in the presence of glucose and peptone, at pH 7.6, temperature 30°C, agitation of 120 rpm and 6 days of incubation by 65 and 37% respectively. Significant reduction in colour and KL content in subsequent incubations is indicative of a co-metabolism mechanism, possibly due to initial utilization of added co-substrates for energy followed by utilization of KL as a co-metabolic. The degradation of KL by bacterium was confirmed by GC-MS analysis indicating formation of several LMWACs such as t-cinnamic acid, 3, 4, 5-trimethoxy benzaldehyde and ferulic acid as degradation products, which were not present in the control (uninoculated) sample. This favours the idea of biochemical modification of the KL polymer to a single monomer unit.