Influence of organic loading rate and temperature fluctuation caused by solar energy heating on food waste anaerobic digestion

Anaerobic digestion, one of the most currently remarkable techniques for biogas production, has provided a method of high organic solid waste disposal. Operating temperature, especially in the winter of northern city, makes biomass degradation less efficient. The microorganisms that take on the role of gas production are greatly affected by temperature. In our study, solar energy was selected for anaerobic digestion and winter was selected as the experimental environment. Anaerobic digestion was performed with solar heating and electric heating separately. Parameters were tested (pH, soluble chemical oxygen demand, total ammonia nitrogen, total volatile fatty acids), and microbial structure was monitored. The volume of methane produced was measured over 60 days. The methane yield differed by 15.92% under different conditions. It is clearly shown that methane yield can be improved by a steady temperature environment. Nevertheless, dominant bacteria and microbial structure did not seem to be much different. This study may provide more energy-saving ideas for winter anaerobic digestion projects in northern regions.

Startup of Demo-Scale Anaerobic Digestion Plant Treating Food Waste Leachate: Process Instability and Recovery

A demo-scale (600 m3 working volume) anaerobic digester treating food waste leachate was monitored during its startup period. The operation strategy was adjusted twice (i.e., three distinct phases) during the operation to recover the process from instability. During the first phase, the organic loading rate (OLR) > 2.7 kg chemical oxygen demand (COD)/m3∙day corresponded to volatile fatty acid (VFA) accumulation along with a decreasing pH, resulting in the drop in biogas yield to 0.43 ± 0.9 m3/kg CODin. During phase 2, fast recovery of this process was aimed at using a sequencing batch operation. One batch cycle (5 to 2 days) consisted of the combined drawing and feeding step (5 h), the reacting step (91 to 17 h), and the settling step (24 h). The duration of the reacting step was determined for each cycle such that (1) the biogas production ceased before the cycle end and (2) the residual VFA concentration was < 1 g/L. In total, 11 cycles were operated with a gradual increase in biogas yield to 0.55 m3/kg CODin with the absence of any sign of system disturbance. After phase 2, the digester was fed at the designed OLR of 4.1 ± 0.3 kg COD/m3∙day. The biogas yield was elevated to 0.58 ± 0.2 m3/kg CODin during phase 3 with the residual VFA concentration maintained at 2.2 ± 0.6 g/L. Methanogen populations, as determined by real-time PCR, did not change significantly throughout the period. These results imply that the adaptation of this process to the OLR of ca. 4 kg COD/m3∙day was not due to the increase in methanogen population but due to the elevation of its activity. Overall, this study suggests that the sequencing batch operation with adjustable cycle duration can be one successful recovery strategy for biogas plants under system instability.

Enhancement of Bioreactor Performance Using Acclimatised Seed Sludge in Anaerobic Treatment of Chicken Slaughterhouse Wastewater: Laboratory Achievement, Energy Recovery, and Its Commercial-Scale Potential

Lack of good management practice of chicken slaughterhouse wastewater (CSWW) has caused pollution into water bodies. In this study, the potential of seed sludge acclimatised modified synthetic wastewater (MSWW) on bioreactor performance and energy recovery of CSWW treatment was investigated. Two sets of upflow anaerobic sludge blanket (UASB) reactors were employed. The seed sludge in UASB 2 was acclimatised with MSWW for 30 days. In UASB 1, no acclimatisation process was undertaken on seed sludge for control purposes. After the acclimatisation process of UASB 2, both reactors were supplied with CSWW under the same condition of organic loading rate (OLR = 0.5 to 6 gCOD/L/d) and mesophilic condition (37 °C). COD removal efficiencies of UASB 2 were >80% all through the steady-state of the OLR applied. Meanwhile, a drastic decrease in overall performance was observed in UASB 1 when the OLR was increased to 3, 4, 5, and 6 gCOD/L/d. Energy recovery from laboratory scale and projected value from commercial-scale bioreactor were 0.056 kWh and 790.49 kWh per day, respectively. Preliminary design of an on-site commercial-scale anaerobic reactor was proposed at a capacity of 60 m3.

Monitoring of Food Waste Anaerobic Digestion Performance: Conventional Co-Substrates vs. Unmarketable Biochar Additions

This study proposed the selection of cost-effective additives generated from different activity sectors to enhance and stabilize the start-up, as well as the transitional phases, of semi-continuous food waste (FW) anaerobic digestion. The results showed that combining agricultural waste mixtures including wheat straw (WS) and cattle manure (CM) boosted the process performance and generated up to 95% higher methane yield compared to the control reactors (mono-digested FW) under an organic loading rate (OLR) range of 2 to 3 kg VS/m³·d. Whereas R3 amended with unmarketable biochar (UBc), to around 10% of the initial fresh mass inserted, showed a significant process enhancement during the transitional phase, and more particularly at an OLR of 4 kg VS/m³·d, it was revealed that under these experimental conditions, FW reactors including UBc showed an increase of 144% in terms of specific biogas yield (SBY) compared to FW reactors fed with agricultural residue. Hence, both agricultural and industrial waste were efficacious when it came to boosting either FW anaerobic performance or AD effluent quality. Although each co-substrate performed under specific experimental conditions, this feature provides decision makers with diverse alternatives to implement a sustainable organic waste management system, conveying sufficient technical details to draw up appropriate designs for the recovery of various types of organic residue.

Effects of a temporary increase in OLR and a simultaneous decrease in HRT on dry anaerobic digestion of OFMSW

The effects of the temporary increase of organic loading rate (OLR) combined with the simultaneous decrease of hydraulic retention time (HRT) on the stability of a pilot scale dry anaerobic digester were investigated. The separately collected organic fraction of municipal solid waste in mesophilic conditions (T = 40°C) was treated. The objective of this study was to verify whether it is possible to feed the digester for short periods, about three consecutive weeks, with higher OLRs and lower HRTs than those considered optimal without generating process failure or long-term instability. Starting from stable operation at a daily OLR of 10.0 kg of total volatile solids (TVS) for digester volume and an HRT of 23 d, the reactor was fed with an OLR of 10.8, 11.7 and 12.5 kg TVS m-3 d-1 corresponding to an HRT of 21, 19 and 18 d, respectively. It was observed that after using an OLR of 10.8 and 11.7 kg TVS m-3 d-1 for 3 weeks with satisfying results, it was possible to restore stable operating conditions at an OLR of 10.0 kg TVS m-3 d-1 in a short time. Otherwise, after using an OLR of 12.5 kg TVS m-3 d-1 the anaerobic digestion was deeply unbalanced and quickly failed. In this latter case, however, it was possible to fully recover and restore the stable conditions of the process within two months.

Influence of earthworm presence and hydraulic loading rate on the performance of vertical flow constructed wetlands

In order to know the behaviour and performance of a vertical flow constructed wetland (VF-CW) operating with earthworm, this study evaluated the earthworm presence linked to hydraulic loading rates applied for domestic wastewater treatment. Two VF-CW units (710 cm², 0.75 m deep, with sand as filter media and planted with Heliconia rostrata) operated with a variable hydraulic and organic loadings rates (200 mm d^-1/123 g COD m^-2 d^-1; 280 mm d^-1/186 g COD m^-2 d^-1; 160 mm d^-1/94 g COD m^-2 d^-1). Although the efficiency of COD load removal was similar (around 70%) for both CWs, the efficiency of total nitrogen load removal was around 95% throughout the evaluated period. The nitrification-denitrification process was identified with and without the presence of earthworm. VF-CW with earthworms showed higher hydraulic conductivity values (from 0.11 to 0.14 m h^-1) compared with the VF-CW wetland without earthworms (0.07-0.09 m h^-1). This study showed that the use of earthworms in CWs can be associated mainly with a preventive measure of clogging, which requires measures to maintain earthworms inside the bed media. Additionally, the earthworm presence has an ingestion mechanism of organic and inorganic solid particles in wastewater which excretes them as finer particles.

Field-scale baffled and biorack hybrid constructed wetland: effect of fluctuating loading rates and recirculation for domestic wastewater treatment

The conventionally used constructed wetlands require modification/s to minimize clogging problems and space requirement. In this study, a field-scale baffled and biorack hybrid constructed wetland (BBHCW) was developed as a part of 42 KLD decentralized wastewater treatment (DWT) system at Walchand College of Engineering, Sangli (M.S.), India for domestic wastewater. Brickbats were used as support medium in the baffled portion and corrugated sheets in biorack. Mixed vegetation of Typha angustifolia and Canna indica was used in both baffled and biorack portions. BBHCW was operated under the dynamic conditions of flow (0.60-9.89 m³/m² day) and strength (0.12-2.12 kg COD/m² day) for 8 months. The performance was assessed for the removal of organic carbon and nitrogen with and without recirculation of treated effluent. Tracer studies showed that the hydraulic efficiency was satisfactory. COD, BOD₃, and TKN removal is possible to an extent of 26.30 ± 1.36, 29.08 ± 2.43, and 19.39 ± 2.27%, respectively, under dynamic conditions. Recirculation enhances the removal efficiency of COD by 5.00-10.00%. However, TKN removal was not significant with or without recirculation. Morphological study showed that vegetation growth was well supported in BBHCW. The discarded corrugated sheets in BR and brickbats in BSFW are the most appropriate low-cost options. The clogging problem is reduced significantly. BBHCW is sturdy enough to absorb shock loading and space requirement can be reduced by judicious choice of HLR and OLR. BBHCW is an alternative to conventionally used sub-surface constructed wetland as a part of DWT. Novelty statementDevelopment of newly configured baffled and biorack hybrid dual-species constructed wetland (BBHCW) for field scale application.Use of discarded brickbat and cement sheets as a new support medium and bioracks.Performance assessment of field-scale BBHCW for the removal of organic carbon (expressed as COD and BOD₃), and nitrogen (expressed as TKN) from domestic wastewater under highly dynamic conditions induced by fluctuating hydraulic loading rate (0.60-9.89 m³/m² day) and organic loading rate (0.12-2.12 kg COD/m² day).

Performance of AnMBR in Treatment of Post-consumer Food Waste: Effect of Hydraulic Retention Time and Organic Loading Rate on Biogas Production and Membrane Fouling

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

Powdered Ceramsite and Powdered Limestone Use in Aerobic Granular Sludge Technology

The effects of two powdered mineral materials (powdered ceramsite and powdered limestone) on aerobic granulation of sludge were evaluated. The experiment was conducted on a laboratory scale bioreactors treating wastewater for 89 days. Three granular sequencing batch reactors (GSBRs) were operated at the lowest optimal organic loading rate (OLR) of 2.55 g COD/(L∙d). In the control reactor (R1), the mean diameter (d) of the biomass ranged from 124.0 to 210.0 µm, and complete granulation was not achieved. However, complete granulation did occur in reactors to which either ceramsite (251.9 µm < d < 783.1 µm) or limestone (246.0 µm < d < 518.9 µm) was added. Both powdered materials served as a ballast for the sludge flocs making up the seed sludge. Ceramsite particles also acted as microcarriers of granule-forming biomass. The granules in the reactors with added powdered materials had nonfibrous and smoother surfaces. The reactor with ceramsite exhibited the highest average efficiencies for COD, total nitrogen, and total phosphorus removal (85.4 ± 5.4%, 56.6 ± 10.2%, and 56.8 ± 9.9%, respectively). By contrast, the average nitrification efficiency was 95.1 ± 12.8%.

Methane potential of fruit and vegetable waste: an evaluation of the semi-continuous anaerobic mono-digestion

The anaerobic digestion (AD) of a high diversity blend of fruit and vegetable waste (FVW) generated in tropical conditions as a single substrate was performed. A continuously stirred tank reactor (CSTR) operated in semi-continuous regime was used for AD. The reactor performance was monitored with gradually increasing organic loading rates (OLRs) from 0.5 up to 5.0 gVS L^-1 d^-1. The biochemical methane potential (BMP) of FVW determined by batch bottles was 360 L_N CH₄ kg_VS^-1, with a biodegradability of 79%. A stable pH with an adequate level of buffering capacity was observed during the entire experiment. Methane yield indicated the best performance at an OLR of 3.0 gVS L^-1 d^-1, with 285 L_N CH₄ kg_VS^-1 added, reaching 79% of BMP. At an OLR over 3.0 gVS L^-1 d^-1 accumulation of volatile fatty acids (VFA) was detected; in particular, propionic acid was monitored, and a decreased methane yield was detected. Biogas production rate was 1.55 L_N L^-1 d^-1 and showed linear increase according to increases in the OLR.

Impact of goethite dosed continuous stirred tank reactor on continuous methane production at different organic loading rates

Iron oxides facilitated anaerobic digestion process has been attracted more and more attention in the renewable energy production area. In the current study, goethite was added into the continuous stirred tank reactor with glucose as the substrate. Effect of the influent organic loading rate (OLR) on the reactor performances was explored. Results showed that goethite promoted the methane production significantly (p < 0.05) when OLR was changed between 1.20 and 1.80 g glucose L^-1  day^-1 . Compared to the control reactor, addition of goethite improved the methane production by13.4%-22.9%. The iron reduction rate had a positive correlation with the methane production rate. Microbial community analysis results showed that OLRs influenced the dominant methanogenic species in the both reactors. Methanothrix, Methanobacterium, Methanosarcina, and Methanocella were dominant under various OLR levels. PRACTITIONER POINTS: Goethite could promote the methanogenic process of glucose in the CSTRs under certain levels of OLRs. Iron reduction rate had a positive correlation with the methane production rate. OLRs influenced the dominant methanogenic species in the goethite-dosed reactors.

Performance Evaluation of a Thermophilic Anaerobic Membrane Bioreactor for Palm Oil Wastewater Treatment

Anaerobic treatment processes have achieved popularity in treating palm oil mill effluent due to its high treatability and biogas generation. The use of externally submerged membranes with anaerobic reactors promotes the retention of the biomass in the reactor. This study was conducted in thermophilic conditions with the Polytetrafluoroethylene hollow fiber (PTFE-HF) membrane which was operated at 55 °C. The reactor was operated at Organic Loading Rates (OLR) of 2, 3, 4, 6, 8, and 10 kg Chemical Oxygen Demand (COD)/m³·d to investigate the treatment performance and the membrane operation. The efficiency of the COD removal achieved by the system was between 93-98%. The highest methane yield achieved was 0.56 m³ CH₄/kg COD_r. The reactor mixed liquor volatile suspended solids (MLVSS) was maintained between 11.1 g/L to 20.9 g/L. A dead-end mode PTFE hollow fiber microfiltration was operated with the constant flux of 3 LMH (L/m²·h) in permeate recirculation mode to separate the clear final effluent and retain the biomass in the reactor. Membrane fouling was one of the limiting factors in the membrane bioreactor application. In this study, organic fouling was observed to be 93% of the total membrane fouling.

Anaerobic co-digestion of municipal sewage sludge and fruit/vegetable waste: effect of different mixtures on digester stability and methane yield

The anaerobic co-digestion of fruit and vegetable waste (FVW) and municipal sewage sludge (MSS) is investigated under mesophilic conditions. This was done at a constant hydraulic retention time (HRT) similar to that typically used at waste water treatment plant digesters, 20 days. The effects on digester performance of the FVW:MSS ratio and the organic loading rate (OLR) were examined. Initially the digester was fed with MSS from wastewater treatment plants (WWTP) with an average OLR of 1.03 kg_VS (m³ d)^-1. The co-digestion of MSS and FVW was performed at various ratios of FVW in the mixture, while increasing the OLRs, from 1.03 to 4.78 kg_VS (m³ d)^-1. The experimental specific methane production (SMP) was 0.303 m³ (kg_VS)^-1 for MSS and 0.403 m³ (kg_VS)^-1 for FVW as single substrate. This value varied for co-digestion with a maximum of 0.445 m³ (kg_VS)^-1 for a FVW:MSS ratio of 40:60. Alkalinity and pH values remain relatively constant regardless the different FVW:MSS ratios fed. As this ratio increases, the removal of the volatile solids (VS) increased from 38.7% to 82%. The average methane content of digester biogas was about 62-64%.

Methanogenic community during the anaerobic digestion of different substrates and organic loading rates

Three anaerobic reactors using pig manure (PM), maize straw (MS), and a mixture of the two as substrates were compared for archaeal community structure and diversity, and for methanogens response to increased organic loading rate (OLR, expressed in the mass of volatile solid (VS)). Methanogenic archaeal richness during codigestion of pig manure with maize straw (ACE: 2412) was greater than that during the others (ACE: 1225, 1467) at an OLR of 4 g L⁻¹ day⁻¹, accompanied by high specific methane yield. Euryarchaeota and Crenarchaeota predominated during overall digestion of different substrates; with relative abundances of 63.5%–99.0% and 1.0%–36.3%, respectively. Methanosarcina was the predominant genus that accounted for 33.7%–79.8% of the archaeal community. The diversity in the PM digester decreased with increase in OLR, but increased in the MS digester. The diversity was stable during the codigestion with increased OLR. The relative abundances of hydrogenotrophic methanogens increased by 2.6 and 2.1 folds; the methanogenic community shifted from acetoclastic to hydrogenotrophic methanogens during digestion of MS, and of the mixture of MS and PM. Canonical correspondence analysis revealed a strong relationship between reactor parameters and methanogenic community.

Application of grey system theory on the influencing parameters of aerobic granulation in SBR

Aerobic granulation is a promising technology for wastewater treatment. Four operational parameters were selected as influencing factors for this study. Aerobic granulation was experimented with three different values of organic loading rate (3, 6 and 9 kg COD m^-3 d^-1), superficial upflow air velocity (SUAV) (2, 3 and 4 cm s^-1), settling time (3, 5 and 10 min) and volume exchange ratio (25%, 50% and 75%) in sequencing batch reactor in nine trials for the optimal performance of aerobic granulation. The influence of compared parameters on five reference parameters (sludge volume index (SVI), time taken for the appearance of granules, size and specific gravity of granules and chemical oxygen demand (COD) removal) was analyzed using grey system theory. The grey relational coefficients and grey entropy relational grade of each parameter were calculated. Hydrodynamic shear force in terms of SUAV was found to have the greatest influence on granule appearance, specific gravity of granules and COD removal efficiency. SVI is greatly affected by settling time. The optimal scopes of all the compared parameters were found.

Production of biogas from co-digestion of livestock and agricultural residues: A case study

This study was undertaken to determine the possible changes in the digester yield and performance for the anaerobic co-digestion under mesophilic conditions of strawberry residues (SRs) together with pig manure (PM). The first part of this paper deals with the digestion of SR as a single substrate. For organic loading rates (OLRs) of 4.4 (g L^-1 d^-1) or less, the experimental specific biogas and methane productions are 0.588 and 0.231 L g^-1, respectively. When higher OLRs (5.5 g L^-1 d^-1) are used the digester fails due to acidification. In the second part, the co-digestion of both residues is explored using a wide variety of SR:PM ratios and OLRs of 5.5 g L^-1 d^-1 with good stability. Therefore, it is demonstrated that co-digestion allows the improvement of the treatment capacity as compared with SR as a single residue. The methane and biogas productions increase as the SR:PM ratio increases. It may be concluded that, when a digester works with a certain OLR, the performance for co-digestion is always better than for single substrates because the presence of PM provides a better stability and the presence of SR improves the biogas and methane production.

Co-metabolic degradation of steroid estrogens by heterotrophic bacteria and nitrifying bacteria in MBRs

Three membrane bioreactors (MBRs) with different carbon/nitrogen ratios were operated in parallel to investigate the effects of heterotrophic bacteria and nitrifying bacteria on the co-metabolic degradation of the steroid estrogens (SEs) estrone (E1) and 17α-ethinylestradiol (EE2). The functional community structures of the MBRs were analyzed using fluorescence in situ hybridization, and correlations between the functional community structures and SE removal efficiencies were established. The results showed that α-Proteobacteria, β-Proteobacteria, and γ-proteobacteria were responsible for the removal of E1, whereas ammonia-oxidizing bacteria, Nitrosomonas sp., Nitrosospira sp., Nitrospira sp., and Nitrobacter sp. were responsible for EE2 removal. Nitrifying activated sludge degraded E1 and EE2 alone, with degradation efficiencies of 71.04 and 65.51%, respectively. Moreover, biodegradation of E1 and EE2 was reduced significantly (by 30.30 and 34.03%, respectively) when nitrification was inhibited. Heterotrophic and nitrifying bacteria were responsible for E1 and EE2 degradation, but nitrification was considered to be the key process in the enhancement of SE degradation. Organic co-metabolism by heterotrophic bacteria had a significant effect on E1 removal, and nitrification co-metabolism by nitrifying bacteria had a significant effect on EE2 removal. These results improve our understanding of the co-metabolic degradation of SEs, which is useful for improving SE removal and guaranteeing the health of aqueous environments.

Pollutant removal performance of an integrated upflow-constructed wetland filled with haydites made of Al-based drinking water treatment residuals

This study examined the pollutants removal performance of an integrated upflow-constructed wetland (IUCW) system in a 1.5 years' continuous operation. The average concentrations of chemical oxygen demand (COD), NH₄-N, total nitrogen (TN), and total phosphorus (TP) in the effluent were 21.9, 1.47, 2.63, and 0.18 mg/L, respectively, which corresponded to 90.1%, 23.3%, 86.1%, and 97.2% removals from the raw water, respectively. The residual concentration of COD was 219 mg/L at start-up and decreased notably to 52.8 mg/L after 50 days of operation. NH₄-N was difficult to remove because the average concentration of dissolved oxygen in the IUCW system was lower than 0.6 mg/L. In contrast, the residual concentrations of both TN and TP in the effluent were stable, with average removal rates as high as 89% and 99%, respectively, at start-up of the system. Changing the organic loading rates from 45.0 g/(m²·day) to 20.0 or 60.0 g/(m²·day) both inhibited the removal of TN. Further study showed that the removal of organic matter mainly occurred within 10-20 cm of the wetland cell. Considering its strong organic, nitrogen, and phosphate removal capacity, the IUCW system was determined to be effective in decentralized wastewater treatment.

Microbial Population Dynamics and Ecosystem Functions of Anoxic/Aerobic Granular Sludge in Sequencing Batch Reactors Operated at Different Organic Loading Rates

The granular sludge process is an effective, low-footprint alternative to conventional activated sludge wastewater treatment. The architecture of the microbial granules allows the co-existence of different functional groups, e.g., nitrifying and denitrifying communities, which permits compact reactor design. However, little is known about the factors influencing community assembly in granular sludge, such as the effects of reactor operation strategies and influent wastewater composition. Here, we analyze the development of the microbiomes in parallel laboratory-scale anoxic/aerobic granular sludge reactors operated at low (0.9 kg m^-3d^-1), moderate (1.9 kg m^-3d^-1) and high (3.7 kg m^-3d^-1) organic loading rates (OLRs) and the same ammonium loading rate (0.2 kg NH₄-N m^-3d^-1) for 84 days. Complete removal of organic carbon and ammonium was achieved in all three reactors after start-up, while the nitrogen removal (denitrification) efficiency increased with the OLR: 0% at low, 38% at moderate, and 66% at high loading rate. The bacterial communities at different loading rates diverged rapidly after start-up and showed less than 50% similarity after 6 days, and below 40% similarity after 84 days. The three reactor microbiomes were dominated by different genera (mainly Meganema, Thauera, Paracoccus, and Zoogloea), but these genera have similar ecosystem functions of EPS production, denitrification and polyhydroxyalkanoate (PHA) storage. Many less abundant but persistent taxa were also detected within these functional groups. The bacterial communities were functionally redundant irrespective of the loading rate applied. At steady-state reactor operation, the identity of the core community members was rather stable, but their relative abundances changed considerably over time. Furthermore, nitrifying bacteria were low in relative abundance and diversity in all reactors, despite their large contribution to nitrogen turnover. The results suggest that the OLR has considerable impact on the composition of the granular sludge communities, but also that the granule communities can be dynamic even at steady-state reactor operation due to high functional redundancy of several key guilds. Knowledge about microbial diversity with specific functional guilds under different operating conditions can be important for engineers to predict the stability of reactor functions during the start-up and continued reactor operation.

[Effects of Organic Loading Rate on Startup Performance of Anaerobic Digestion with Vinegar Residues]

Biochemical methane potential experiments were conducted to investigate the effects of organic loading rate on the performance of anaerobic digesters with vinegar residues. According to the comparisons of methane production and liquid phase compositions, as well as thermogravimetry, X-ray Diffraction and infrared spectroscopy analyses, the conclusions could be drawn that:①Lower organic loading rate was better to mitigate the accumulation of VFAs and pH decrease during the hydrolysis and acidification of organic matters, which consequently improved methane production. When the inoculum to substrate ratio was 1:1[organic loading rate of 1.78 g·(L·d)^-1, pH=7.60], the cumulative methane production was the highest, reaching 2249.7 mL, and the performance of the digesters was stable. The VFAs content increased with the increase of the organic loading rate, leading to the suppression and further the stop of methane production. And when the inoculum to substrate ratio was 1:4[organic loading rate of 7.12 g·(L·d)^-1, pH=5.52], the simultaneous generation of acetate and lactic acids could be achieved at 8000 mg·L^-1 and 2650 mg·L^-1, respectively. ② As vinegar residues were short-range ordered with microcrystalline structure or mainly contained amorphous substances, they were more biodegradable than feedstocks such as corn stalk. During the anaerobic digestion processes, the degradation rates of lignin, cellulose and hemicellulose increased with the decrease of organic loading rate.

[Enhanced Pollutant Removal Performance of an Integrated Biological Settling Tank from Micro-polluted Water Bodies]

To improve the capacity of present drinking water purification process on the removal of soluble pollutants and solve the problem of large area requirement and single function existing in the application of horizontal sedimentation tank, a novel biological settling tank was developed based on the designing concepts of rotating biological disk and sedimentation tank. Experimental results showed that the usage of rotating biological disk did not have notable effects on the turbidity removal capacity of the horizontal sedimentation tank. When the organic loading rate was 0.46 g·(m²·d)^-1, the removal rates of organic pollutants, NH₄⁺-N, TN, and TP were determined to be 81.4%, 95.0%, 21.1% and 86.0%, respectively. Further study showed that denitrification and dephosphorization processes competed for the limited carbon source existing in the water phase. With the increase of organic loading rate in the raw water, the removal rate of TP was improved. Meanwhile, the concentrations of organic matters and NH₄⁺-N in the settled water were not affected, which indicated that the biological settling tank showed a capacity in resisting organic loading rate shock and could be used in the enhanced pollutant removal in treating micro-polluted water.

Effects and optimization of the use of biochar in anaerobic digestion of food wastes

The addition of various amounts of biochar to anaerobic digestion of food wastes at different ratios of inoculum to substrate (ISR) was investigated to evaluate the effect of biochar as a functional additive and to optimize the additive dosage of biochar. The biochar treatments at ISR 2, 1, and 0.8 shortened the lag phase of digestion by -20.0%-10.9%, 43.3%-54.4%, and 36.3%-54.0%, and raised the maximum methane production rate by 100%-275%, 100%-133.3%, and 33.3%-100%, respectively, compared to control without biochar. Biochar also enhanced the degradation rate of dissolved organics and volatile fatty acids. Furthermore, the amount of biochar with best effectiveness at ISR = 2, 1, and 0.8 was 2.5, 0.625, and 0.5 g g(-1)-waste, respectively. Therefore, the effectiveness of biochar depended on the additive amount of biochar and at the same time the inoculum amount, implying a complementary role of abiotic biochar to biotic inoculum.

Characterization of wastewater treatment by two microbial fuel cells in continuous flow operation

A two serially connected single-chamber microbial fuel cell (MFC) was applied to the treatment of diluted molasses wastewater in a continuous operation mode. In addition, the effect of series and parallel connection between the anodes and the cathode on power generation was investigated experimentally. The two serially connected MFC process achieved 79.8% of chemical oxygen demand removal and 11.6% of Coulombic efficiency when the hydraulic retention time of the whole process was 26 h. The power densities were 0.54, 0.34 and 0.40 W m(-3) when electrodes were in individual connection, serial connection and parallel connection modes, respectively. A high open circuit voltage was obtained in the serial connection. Power density decreased at low organic loading rates (OLR) due to the shortage of organic matter. Power generation efficiency tended to decrease as a result of enhancement of methane fermentation at high OLRs. Therefore, high power density and efficiency can be achieved by using a suitable OLR range.

Addressing case specific biogas plant tasks: industry oriented methane yields derived from 5L Automatic Methane Potential Test Systems in batch or semi-continuous tests using realistic inocula, substrate particle sizes and organic loading

The primary aim of the study was to develop and validate an in-house upscale of Automatic Methane Potential Test System II for studying real-time inocula and real-scale substrates in batch, codigestion and enzyme enhanced hydrolysis experiments, in addition to semi-continuous operation of the developed equipment and experiments testing inoculum functional quality. The successful upscale to 5L enabled comparison of different process configurations in shorter preparation times with acceptable accuracy and high-through put intended for industrial decision making. The adoption of the same scales, equipment and methodologies in batch and semi-continuous tests mirroring those at full scale biogas plants resulted in matching methane yields between the two laboratory tests and full-scale, confirming thus the increased decision making value of the approach for industrial operations.

Generalised modelling approach for anaerobic co-digestion of fermentable substrates

A general methodology to implement fermentable soluble substrates in the IWA Anaerobic Digestion Model No. 1 (ADM1) that extends its application to anaerobic co-digestion of multiple substrates is presented. The approach considers the fermentation of new soluble substrates, not originally described in ADM1, as channelled through mass- and electron-balanced sugar fermentation equivalent reactions, and that fermentable substrates are degraded by a generic group of fermenters instead of the original ADM1 sugar fermenters. Therefore, no additional microbial group state is required. An additional term that modifies the ADM1 sugar fermentation kinetics equation was included to account for the competition among multiple substrates to be degraded by a particular biomass group. The model was validated at pilot scale treating a blend of pig manure (soluble fraction), wine and gelatine at mesophilic conditions. Only the ADM1 acetoclastic ammonia inhibition parameter was calibrated to obtain consistent model prediction of gas and liquid composition.

Comparison of methanogenic community structure and anaerobic process performance treating swine wastewater between pilot and optimized lab scale bioreactors

To investigate methanogenic community structure and process performance of anaerobic digestion treating swine wastewater at different scale, a pilot plant with 20 m(3) of effective working volume and lab scale methanogenic digester with 6L working volume were operated for 71 days and 6 turnover periods, respectively. During the steady state of anaerobic digestion, COD and VS removal efficiency in pilot plant were 65.3±3.2, 51.6±4.3%, respectively, which was similar to those in lab scale. However, calculated VFAs removal efficiency and methane yield were lower in pilot plant than in lab scale digester. Also, organics removal efficiencies, which consist of total carbohydrates, proteins, and lipids, were different between pilot and lab scale. These results were thought to be due to the ratio of carbohydrates to proteins in the raw swine wastewater. As a result of qualitative microbial analysis, Methanoculleus receptaculii, and Methanoculleus bourgensis, were commonly concerned with methane production.