Enhanced biomethanation of kitchen waste by different pre-treatments

Five different pre-treatments were investigated to enhance the solubilisation and anaerobic biodegradability of kitchen waste (KW) in thermophilic batch and continuous tests. In the batch solubilisation tests, the highest and the lowest solubilisation efficiency were achieved with the thermo-acid and the pressure-depressure pre-treatments, respectively. However, in the batch biodegradability tests, the highest cumulative biogas production was obtained with the pressure-depressure method. In the continuous tests, the best performance in terms of an acceptable biogas production efficiency of 60% and stable in-reactor COD_s and VFA concentrations corresponded to the pressure-depressure reactor, followed by freeze-thaw, acid, thermo-acid, thermo and control. The maximum OLR (5 g COD L⁻¹ d⁻¹) applied in the pressure-depressure and freeze-thaw reactors almost doubled the control reactor. From the overall analysis, the freeze-thaw pre-treatment was the most profitable process with a net potential profit of around 11.5 € ton⁻¹ KW.     

Pentachlorophenol (PCP) dechlorination in horizontal-flow anaerobic immobilized biomass (HAIB) reactors

This study verifies the potential applicability of horizontal-flow anaerobic immobilized biomass (HAIB) reactors to pentachlorophenol (PCP) dechlorination. Two bench-scale HAIB reactors (R1 and R2) were filled with cubic polyurethane foam matrices containing immobilized anaerobic sludge. The reactors were then continuously fed with synthetic wastewater consisting of PCP, glucose, acetic acid, and formic acid as co-substrates for PCP anaerobic degradation. Before being immobilized in polyurethane foam matrices, the biomass was exposed to wastewater containing PCP in reactors fed at a semi-continuous rate of 2.0 μg PCP g⁻¹ VS. The applied PCP loading rate was increased from 0.05 to 2.59 mg PCP l⁻¹ day⁻¹ for R1, and from 0.06 to 4.15 mg PCP l⁻¹ day⁻¹ for R2. The organic loading rates (OLR) were 1.1 and 1.7 kg COD m⁻³ day⁻¹ at hydraulic retention times (HRT) of 24 h for R1 and 18 h for R2. Under such conditions, chemical oxygen demand (COD) removal efficiencies of up to 98% were achieved in the HAIB reactors. Both reactors exhibited the ability to remove 97% of the loaded PCP. Dichlorophenol (DCP) was the primary chlorophenol detected in the effluent. The adsorption of PCP and metabolites formed during PCP degradation in the packed bed was negligible for PCP removal efficiency.     

Effect of organic loading rate on VFA production, organic matter removal and microbial activity of a two-stage thermophilic anaerobic membrane bioreactor

This study focused on the VFA (volatile fatty acid) profile variation with organic loading rate (OLR) of a two stage thermophilic anaerobic membrane bioreactor (TAnMBR). The two stage TAnMBR treating high strength molasses-based synthetic wastewater was operated under a side-stream partial sedimentation mode at 55 °C. Reactor performances were studied at different OLR ranging from 5 to 12 kg COD m⁻³ d⁻¹. Operational performance of TAnMBR was monitored by assessing biological activity, organic removal efficiency, and VFA. The major intermediate products of anaerobic digestion were identified as acetate, propionate, iso-butyrate, n-butyrate and valerate. Among them acetate and n-butyrate were identified as the most abundant components. Increase of OLR changes the predominant VFA type from acetic acid to n-butyric acid and the total VFA concentration was increased with increased OLR. Moreover, increased OLR increased organic removal efficiency up to second loading rate and dropped in third loading rate while biological activity was increased continuously.     

Feasibility of biogas production from anaerobic co-digestion of herbal-extraction residues with swine manure

The objective of this work was to examine the feasibility of biogas production from the anaerobic co-digestion of herbal-extraction residues with swine manure. Batch and semi-continuous experiments were carried out under mesophilic anaerobic conditions. Batch experiments revealed that the highest specific biogas yield was 294 mL CH₄ g⁻¹ volatile solids added, obtained at 50% of herbal-extraction residues and 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Specific methane yield from swine manure alone was 207 mL CH₄ g⁻¹ volatile solid added d⁻¹ at 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Furthermore, specific methane yields were 162, 180 and 220 mL CH₄ g⁻¹ volatile solids added d⁻¹ for the reactors co-digesting mixtures with 10%, 25% and 50% herbal-extraction residues, respectively. These results suggested that biogas production could be enhanced efficiently by the anaerobic co-digestion of herbal-extraction residues with swine manure.     

Effect of chitosan on UASB treating POME during a transition from mesophilic to thermophilic conditions

The effects of chitosan addition on treatment of palm oil mill effluent were investigated using two lab-scale upflow anaerobic sludge bed (UASB) reactors: (1) with chitosan addition at the dosage of 2 mg chitosan per g volatile suspended solids on the first day of the operation (R1), (2) without chitosan addition (the control, R2). The reactors were inoculated with mesophilic anaerobic sludge which was acclimatized to a thermophilic condition with a stepwise temperature increase of 5 °C from 37 to 57 °C. The OLR ranged from 2.23 to 9.47 kg COD m⁻³ day⁻¹. The difference in biogas production rate increased from non-significant to 18% different. The effluent volatile suspended solids of R1 was 65 mg l⁻¹ lower than that of R2 on Day 123. 16S rRNA targeted denaturing gradient gel electrophoresis (DGGE) fingerprints of microbial community indicated that some methanogens in the genus Methanosaeta can be detected in R1 but not in R2.     

Evaluation of the hydrolytic–acidogenic step of a two-stage mesophilic anaerobic digestion process of sunflower oil cake

The influence of the hydraulic retention time (HRT) and organic loading rate (OLR) on the performance of the hydrolytic–acidogenic step of a two-stage anaerobic digestion process of sunflower oil cake (SuOC) were assessed. The experiments were performed in laboratory-scale completely stirred tank reactors at mesophilic (35 °C) temperature. Six OLR (ranging from 4 to 9 g VS L⁻¹ d⁻¹) for four HRTs (8, 10, 12 and 15 days) were tested to check the effect of each operational variable. Based on the results obtained, it can be concluded that the hydrolysis yields obtained for all HRTs and OLRs assayed were in the range of 20.5–30.1%. In addition, the acidification degree of the substrate was mainly influenced by the OLR but not by the HRTs, the highest value (83.8%) being achieved for an HRT of 10 days and an OLR of 6 g VS L⁻¹ d⁻¹.     

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.     

Two-stage anaerobic digestion of biodegradable municipal solid waste using a rotating drum mesh filter bioreactor and anaerobic filter

A rotating drum mesh filter bioreactor (RDMFBR) with a 100 μm mesh coupled to an anaerobic filter was used for the anaerobic digestion of biodegradable municipal solid waste (BMW). Duplicate systems were operated for 72 days at an organic loading rate (OLR) of 7.5 gVS l⁻¹ d⁻¹. Early in the experiment most of the methane was produced in the 2nd stage. This situation gradually reversed as methanogenesis became established in the 1st stage digester, which eventually produced 86–87% of the total system methane. The total methane production was 0.2 l g⁻¹ VS_added with 60–62% volatile solids destruction. No fouling was experienced during the experiment at a transmembrane flux rate of 3.5 l m⁻² h⁻¹. The system proved to be robust and stably adjusted to a shock loading increase to 15 gVS l⁻¹ d⁻¹, although this reduced the overall methane production to 0.15 l g⁻¹ VS_added.     

Optimising the biogas production from leather fleshing waste by co-digestion with MSW

Waste from the leather industry, known as limed leather fleshing (LF), has a low C:N (3.2) and an alkaline pH of 11.4. This is a major disadvantage for anaerobic digestion due to ammonia toxicity for methanogenesis. This study describes co-digestion of LF with biodegradable fraction of municipal solids waste optimised over a range of C:N and pH to minimise ammonia and to maximise biogas yield. The optimum conditions were found with a blend that provided C:N of 15 and pH of 6.5 and the cumulative biogas yield increased from 560 mL using LF fraction alone, to 6518 mL with optimum blend. At higher pH of 8.5, unionised ammonia was high (2473 mg L⁻¹) coincided with poor biogas yield (47 mL d⁻¹) that confirms ammonia toxicity. By contrast at a pH of 4.5 the ammonia was minimum (510 mg L⁻¹), but high VFA (26,803 mg L⁻¹) inhibited the methanogens. Biomass activity measured using ATP correlated well with biogas yield as reported previously.     

Performance and spatial community succession of an anaerobic baffled reactor treating acetone-butanol-ethanol fermentation wastewater

An anaerobic baffled reactor with four compartments (C1-C4) was successfully used for treatment of acetone-butanol-ethanol fermentation wastewater and methane production. The chemical oxygen demand (COD) removal efficiency was 88.2% with a CH₄ yield of 0.25 L/(g COD_removed) when organic loading rate (OLR) was 5.4 kg COD m⁻³ d⁻¹. C1 played the most important role in solvents (acetone, butanol and ethanol) and COD removal. Community structure of C2 was similar to that in C1 at stage 3 with higher OLR, but was similar to those in C3 and C4 at stages 1-2 with lower OLR. This community variation in C2 was consistent with its increased role in COD and solvent removal at stage 3. During community succession from C1 to C4 at stage 3, abundance of Firmicutes (especially OTUs ABRB07 and ABRB10) and Methanoculleus decreased, while Bacteroidetes and Methanocorpusculum became dominant. Thus, ABRB07 coupled with Methanoculleus and/or acetogen (ABRB10) may be key species for solvents degradation.     

Maximum removal rate of propionic acid as a sole carbon source in UASB reactors and the importance of the macro- and micro-nutrients stimulation

The maximum propionic acid (HPr) removal rate (R_HPr) was investigated in two lab-scale Upflow Anaerobic Sludge Bed (UASB) reactors. Two feeding strategies were applied by modifying the hydraulic retention time (HRT) in the UASB_HRT and the influent HPr concentration in the UASB_HPr, respectively. The experiment was divided into three main phases: phase 1, influent with only HPr; phase 2, HPr with macro-nutrients supplementation and phase 3, HPr with macro- and micro-nutrients supplementation. During phase 1, the maximum R_HPr achieved was less than 3 g HPr-COD L⁻¹ d⁻¹ in both reactors. However, the subsequent supplementation of macro- and micro-nutrients during phases 2 and 3 allowed to increase the R_HPr up to 18.1 and 32.8 g HPr-COD L⁻¹ d⁻¹, respectively, corresponding with an HRT of 0.5 h in the UASB_HRT and an influent HPr concentration of 10.5 g HPr-COD L⁻¹ in the UASB_HPr. Therefore, the high operational capacity of these reactor systems, specifically converting HPr with high throughput and high influent HPr level, was demonstrated. Moreover, the presence of macro- and micro-nutrients is clearly essential for stable and high HPr removal in anaerobic digestion.     

Molecular microbial ecology of stable versus failing rice straw anaerobic digesters

Waste rice straw (RS) is generated in massive quantities around the world and is often burned, creating greenhouse gas and air quality problems. Anaerobic digestion (AD) may be a better option for RS management, but RS is presumed to be comparatively refractory under anaerobic conditions without pre-treatment or co-substrates. However, this presumption assumes frequent reactor feeding regimes but less frequent feeding may be better for RS due to slow hydrolysis rates. Here, we assess how feeding frequency (FF) and organic loading rate (OLR) impacts microbial communities and biogas production in RS AD reactors. Using 16S rDNA amplicon sequencing and bioinformatics, microbial communities from five bench-scale bioreactors were characterized. At low OLR (1.0 g VS l⁻¹ day⁻¹), infrequently fed units (once every 21 days) had higher specific biogas yields than more frequent feeding (five in 7 days), although microbial community diversities were statistically similar (P > 0.05; ANOVA with Tukey comparison). In contrast, an increase in OLR to 2.0 g VS l⁻¹ day⁻¹ significantly changed Archaeal and fermenting Eubacterial sub-communities and the least frequency fed reactors failed. ‘Stable’ reactors were dominated by Methanobacterium, Methanosarcina and diverse Bacteroidetes, whereas ‘failed’ reactors saw shifts towards Clostridia and Christensenellaceae among fermenters and reduced methanogen abundances. Overall, OLR impacted RS AD microbial communities more than FF. However, combining infrequent feeding and lower OLRs may be better for RS AD because of higher specific yields.     

Treatment of industrial wastewater with two-stage constructed wetlands planted with Typha latifolia and Phragmites australis

Industrial wastewater treatment comprises several processes to fulfill the discharge permits or to enable the reuse of wastewater. For tannery wastewater, constructed wetlands (CWs) may be an interesting treatment option. Two-stage series of horizontal subsurface flow CWs with Phragmites australis (UP series) and Typha latifolia (UT series) provided high removal of organics from tannery wastewater, up to 88% of biochemical oxygen demand (BOD₅) (from an inlet of 420 to 1000 mg L⁻¹) and 92% of chemical oxygen demand (COD) (from an inlet of 808 to 2449 mg L⁻¹), and of other contaminants, such as nitrogen, operating at hydraulic retention times of 2, 5 and 7 days. No significant (P < 0.05) differences in performance were found between both the series. Overall mass removals of up to 1294 kg COD ha⁻¹ d⁻¹ and 529 kg BOD₅ ha⁻¹ d⁻¹ were achieved for a loading ranging from 242 to 1925 kg COD ha⁻¹ d⁻¹ and from 126 to 900 kg BOD₅ ha⁻¹ d⁻¹. Plants were resilient to the conditions imposed, however P. australis exceeded T. latifolia in terms of propagation.     

Laboratory-scale ultrasound pre-treated digestion of sludge: Heat and energy balance

The objective of this work was to maximize the digestibility of biological sludge to elucidate the feasibility of a new sludge management strategy to recover good quality sludge for agricultural use. The combined effects of organic loading rates (from 0.7 to 2.8 g VS L⁻¹ d⁻¹) and the degree of disintegration by anaerobic digestion of sonicated activated sludge were discussed, and the thermal and energetic balances were evaluated. Despite low sonication inputs, sludge digestion performance improved in terms of solids degradation and biogas production depending on the soluble organic load. The biogas production by sonicated sludge was higher (up to 30%) with respect to the control. Filterability improved during digestion of sonicated sludge at medium OLR due to a significant abatement of the fines. Thermal balances indicated that sonication may be a proper system to guarantee self-sustaining WAS mesophilic digestion. Nevertheless, thickening is a pre-requisite to achieve a positive energy balance.     

Influence of food colorant and initial COD concentration on the efficiencies of micro-aerobic sequencing batch reactor (micro-aerobic SBR) for casein recovery under non-sterile condition by Lactobacillus casei TISTR 1500

The acid biocoagulants produced from non-sterile lactic acid fermentation by Lactobacillus casei TISTR 1500 were used to settle colloidal protein, mainly casein, at the isoelectric point in dairy effluent prior to secondary treatment. High concentration of azo dye (Ponceau 4R) in the dairy wastewater and the stress of starvation decreased the efficiencies of the micro-aerobic SBR. Consequently, low casein recovery obtained and organic removal suffered a decline. The number of lactic acid bacteria (LAB) also declined from log 7.4 to log 5.30 in the system fed with 400 mg L⁻¹ of the dye containing wastewater. The recovery of the system, however, showed that 25,000 mg COD L⁻¹ influent with 200 mg L⁻¹ of the dye maintained the growth of LAB in the range of log 7.74–8.12, with lactic and acetic production (2597 and 197 mg L⁻¹) and 83% protein removal. The results in this study suggested that the inhibitory effects were compensated with high organic content feeding.     

Propionic acid fermentation from glycerol: comparison with conventional substrates

Instead of the conventional carbon sources used for propionic acid biosynthesis, the utilization of glycerol is considered here, since the metabolic pathway involved in the conversion of glycerol to propionic acid is redox-neutral and energetic. Three strains, Propionibacterium acidipropionici, Propionibacterium acnes and Clostridium propionicum were tested for their ability to convert glycerol to propionic acid during batch fermentation with initially 20 g/l glycerol. P. acidipropionici showed higher efficiency in terms of fermentation time and conversion yield than did the other strains. The fermentation profile of this bacterium consisted in propionic acid as the major product (0.844 mol/mol), and in minimal by-products: succinic (0.055 mol/mol), acetic (0.023 mol/mol) and formic (0.020 mol/mol) acids and n-propanol (0.036 mol/mol). The overall propionic acid productivity was 0.18 g l⁻¹h⁻¹. A comparative study with glucose and lactic acid as carbon sources showed both less diversity in end-product composition and a 17% and 13% lower propionic acid conversion yield respectively than with glycerol. Increasing the initial glycerol concentration resulted in an enhanced productivity up to 0.36 g l⁻¹h⁻¹ and in a maximal propionic acid concentration of 42 g/l, while a slight decrease of the conversion yield was noticed. Such a propionic acid production rate was similar or higher than the values obtained with lactic acid (0.35 g l⁻¹h⁻¹) or glucose (0.28 g l⁻¹h⁻¹). These results demonstrated that glycerol is a carbon source of interest for propionic acid production. Received: 15 July 1996 / Received revision: 11 November 1996 / Accepted: 11 November 1996     

The role of phase separation and feed cycle length in leach beds coupled to methanogenic reactors for digestion of a solid substrate (Part 1): Optimisation of reactors' performance

A two-phase system composed by a leach bed and a methanogenic reactor was modified for the first time to improve volumetric substrate degradation and methane yields from a complex substrate (maize; Zeamays). The system, which was operated for consecutive feed cycles of different durations for 120 days, was highly flexible and its performance improved by altering operational conditions. Daily substrate degradation was higher the shorter the feed cycle, reaching 8.5 g TS_destroyed d⁻¹ (7-day feed cycle) but the overall substrate degradation was higher by up to 55% when longer feed cycles (14 and 28 days) were applied. The same occurred with volumetric methane yields, reaching 0.839 m³ (m³)⁻¹ d⁻¹. The system performed better than others on specific methane yields, reaching 0.434 m³ kg⁻¹ TS_added, in the 14-day and 28-day systems. The UASB and AF designs performed similarly as second stage reactors on methane yields, SCOD and VFA removal efficiencies.     

Autotrophic denitrification using hydrogen generated from metallic iron corrosion

Hydrogenotrophic denitrification was demonstrated using hydrogen generated from anoxic corrosion of metallic iron. For this purpose, a mixture of hydrogenated water and nitrate solution was used as reactor feed. A semi-batch reactor with nitrate loading of 2000 mg m⁻³ d⁻¹ and hydraulic retention time (HRT) of 50 days produced effluent with nitrate concentration of 0.27 mg N L⁻¹ (99% nitrate removal). A continuous flow reactor with nitrate loading of 28.9 mg m⁻³ d⁻¹ and HRT of 15.6 days produced effluent with nitrate concentration of ∼0.025 mg N L⁻¹ (95% nitrate removal). In both cases, the concentration of nitrate degradation by-products, viz., ammonia and nitrite, were below detection limits. The rate of denitrification in the reactors was controlled by hydrogen availability, and hence to operate such reactors at higher nitrate loading rates and/or lower HRT than reported in the present study, hydrogen concentration in the hydrogenated water must be significantly increased.     

Effect of seed sludge and operation conditions on performance and archaeal community structure of low-temperature anaerobic solvent-degrading bioreactors

Two laboratory-scale expanded granular sludge bed (EGSB) anaerobic bioreactors (R1 and R2) were inoculated with biomass from different mesophilic (37 °C) treatment plants, and used for the treatment of an organic solvent-based wastewater at 9–14 °C at applied organic loading rates (OLRs) of 1.2–3.6 kg chemical oxygen demand (COD) m⁻³ d⁻¹. Replicated treatment performance was observed at 10–14 °C, which suggested the feasibility of the process at pilot-scale. Stable and efficient COD removal, along with high methane productivity, was demonstrated at 9 °C at an applied OLR of 2.4 kg COD m⁻³ d⁻¹. Clonal libraries and fluorescence in situ hybridization (FISH) indicated that the seed sludges were dominated (>60%) by acetoclastic Methanosaeta-like organisms. Specific methanogenic activity (SMA) profiles indicated shifts in the physiological profiles of R1 and R2 biomass, including the development of psychrotolerant methanogenic activity. Acetoclastic methanogenesis represented the primary route of methane production in R1 and R2, which is in contrast with several previous reports from low-temperature bioreactor trials. A reduction in the abundance of Methanosaeta-like clones (R2), along with the detection of hydrogenotrophic methanogenic species, coincided with altered granule (sludge) morphology and the development of hydrogenotrophic SMA after prolonged operation at 9 °C.