Anaerobic organic acid production of food waste in once-a-day feeding and drawing-off bioreactor

Acidogenesis of food waste was studied in a 2-L reactor with semi-continuous mode operation (once-a-day feeding and draw-off) for maximum 65 days to examine optimal volatile acid compositions for biological nitrogen removal (BNR) and enhanced biological phosphorus removal (ENPR). Various operational parameters of hydraulic retention time (HRT), organic loading rate (ORL), pH and temperature were investigated for soluble chemical oxygen demand (SCOD), volatile fatty acid composition, nitrogen and phosphate. The yields (gTVFA/g VS) and the volumetric productivity (gTVFA/d L) increased with HRT from 0.26-0.32, 1.25-1.50 (at 4 days) to 0.36-0.39, 1.71-1.83 (at 12 days). However, the acetate fraction (%) decreased with HRT from 35.7-37.5 at 4 days to 23.5-25 at 12 days. The yields decreased with increase of organic loading from 0.34-0.37 at 5 g/L d to 0.29-0.30 at 13 g/L d and the productivity increased from 1.63-1.65 to 3.61-3.75. The yield and productivity were highest at 35 degrees C among 25, 35 and 45 degrees C. The yield and productivity at pH 5.5 and 6.0 were best and very similar to each other. The condition of 35 degrees C, pH 6.0, HRT 8 days, ORL 9 g/L d resulted in TVFA, SCOD, acetate and butyrate of 25, 39.5, 12 and 5.25 g/L, respectively.     

生物强化污泥厌氧发酵产酸研究进展*

污泥厌氧发酵生产挥发性脂肪酸相较产甲烷,是更具应用价值的污泥稳定途径及资源化利用方式,得到国内外学者的普遍重视。考虑到产酸量低和产酸过程的不稳定性是限制污泥发酵产酸的主要问题,采用生物强化方法实现挥发性脂肪酸的大量积累,与物理和化学方法相比,具有成本低、无二次污染等优点。根据生物强化制剂的类型,归纳了微生物纯培养物、微生物混合培养物及生物酶强化对污泥厌氧发酵产酸的影响,并在此基础上对生物强化技术控制污泥定向产酸、调控奇偶数碳比率等方面的应用进行讨论。此外,分析了影响挥发性脂肪酸产量和组分的因素,如pH、温度、底物、水力停留时间和污泥龄等。最后对生物强化技术的发展方向进行了展望,以期为深入探究污泥资源化利用提供借鉴。     

VFAs bioproduction from waste activated sludge by coupling pretreatments with Agaricus bisporus substrates conditioning

A novel strategy for improving volatile fatty acids (VFAs) bioproduction from waste activated sludge (WAS) was developed by coupling pretreatments with conditioning (CPC). Agaricus bisporus substrate (ABS) was used as external carbohydrate additive source of conditioning step. Pretreatment was studied in three ways: alkaline, alkaline-thermal and ultrasonic. WAS hydrolysis and protein degradation was distinctly improved by CPC treatments, resulting in a considerable enhancement of VFAs yield. The maximal VFAs yield was 614 ± 71, 712 ± 49 and 598 ± 19 mg COD/g VSS at pre-optimized alkaline, alkaline-thermal and ultrasonic CPC treatments, respectively, with an increase of 35%, 50% and 38% compared to the yields of pretreated WAS fermentation. Fourier transformed infrared spectroscopy and three-dimensional excitation-emission matrix fluorescence spectroscopy indicated that a synergistic effect occurred in co-digesting WAS and ABS. The conditioning of carbohydrate with feasible pretreatment provided large room for the digestibility improvement and the operation cost reduction in the whole WAS treatment system.     

Influence of inoculum activity on the bio-methanization of a kitchen waste under different waste/inoculum ratios

The use of a granular inoculum prevented acidification during the anaerobic batch biodegradation of a kitchen waste for waste/inoculum ratios in the range of 0.5–2.3 g VS/g VS, when the alkalinity/COD ratio was 37 mg NaHCO₃/g COD. In similar experiments but using a suspended sludge with a significantly lower activity, the methane production rates and the biodegradability were significantly lower and the pH decreased below 5.5 at the waste/inoculum ratio of 2.3 g VS/g VS. When the added alkalinity was decreased to 2 mg NaHCO₃/g COD, the ratio waste/inoculum was clearly more important than the inoculum activity, since, irrespective of the sludge used, acidification occurred at waste/inoculum ratios higher than 0.5 g VS/g VS. The advantage of using granular sludge was further investigated in order to define reasonable condition of waste/inoculum ratio and added alkalinity that could be applied in practice. For a waste/inoculum ratio of 1.35, there were no significant differences between the results obtained for the biodegradability and maximum methane production rate (MMPR), when the alkalinity decreased from 44 to 22 mg NaHCO₃/g COD.     

Volatile fatty acids accumulation and rhamnolipid generation in situ from waste activated sludge fermentation stimulated by external rhamnolipid addition

The solubilization and acidification of waste activated sludge (WAS) were apparently enhanced by external rhamnolipid (RL) addition. The maximum solute carbohydrate concentrations increased linearly from 48 ± 5 mg COD L⁻¹ in the un-pretreated WAS (blank) to 566 ± 19 mg COD L⁻¹, and protein increased from 1050 ± 8 to 3493 ± 16 mg COD L⁻¹ at RL dosage of 0.10 g g⁻¹ TSS. The highest VFAs concentration peaked at 3840 mg COD L⁻¹ at RL dosage of 0.04 g g⁻¹ TSS, which was 4.24-fold higher than the blank test. RL was generated in situ during WAS fermentation when external RL was added. It was detected that RL concentration was increased from initial 880 ± 92 mg L⁻¹ to 1312 ± 7 mg L⁻¹ at the end of 96 h with RL dosage of 0.04 g g⁻¹ TSS, which was increased to 1.49-fold. Meanwhile, methane production was notably reduced to a quite low level of 2.0 mL CH₄ g⁻¹ VSS, showing effective inhibition of methanogens by RL (58.8 mL CH₄ g⁻¹ VSS in the blank). In addition, the activity of hydrolytic enzymes (protease and α-glucosidase) was enhanced accordingly. VFAs accumulation and RL generation in situ demonstrated that the additional RL substantially performed enhanced biological effects for waste activated sludge fermentation.     

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.     

Acidogenic fermentation of proteinaceous solid waste and characterization of different bioconversion stages and extracellular products

The purpose of this study was to investigate hydrolysis of animal fleshing (ANFL), a predominant tannery solid waste and to characterize the acetogenic fermentation products of anaerobic digestion. The acidogenic digestibility of the tannery solid wastes were evaluated up to 120 h using batch anaerobic digestion tests performed under mesophilic condition at 37 degrees C. The degradation of ANFL starts with non-fibrillar proteins and proceeds with fibrillar proteins. The release of aliphatic amino acid in the early stages of hydrolysis (24 h) and followed by aromatic amino acids (24-72 h) were evidenced by HPLC analysis. The maximum production of propionic and valeric acid were observed in 72 h followed by rapid increase in acetic acid in 96 h using GC-MS. Breakdown of ANFL and formations of other metabolites were evidenced by FT-IR and (1)H-NMR spectroscopy.     

Anaerobic digestion of source-segregated domestic food waste: Performance assessment by mass and energy balance

An anaerobic digester receiving food waste collected mainly from domestic kitchens was monitored over a period of 426 days. During this time information was gathered on the waste input material, the biogas production, and the digestate characteristics. A mass balance accounted for over 90% of the material entering the plant leaving as gaseous or digestate products. A comprehensive energy balance for the same period showed that for each tonne of input material the potential recoverable energy was 405 kWh. Biogas production in the digester was stable at 642 m³ tonne⁻¹ VS added with a methane content of around 62%. The nitrogen in the food waste input was on average 8.9 kg tonne⁻¹. This led to a high ammonia concentration in the digester which may have been responsible for the accumulation of volatile fatty acids that was also observed.     

Short communication: Butyrate-degrading syntrophic culture from an anaerobic digester treating cattle waste

A co-culture of bacteria responsible for the conversion of butyrate to methane and CO₂ was isolated from a cattle-waste treatment plant. The non-methanogenic partner of the co-culture was Syntrophomonas wolfei and the methanogenic partner was Methanobacterium formicicum. Although butyrate degradation occurred at pH<6.0 and below 45°C, methanogenesis was observed at pH>6.5 and above 40°C.     

Influence of carbohydrates and proteins concentration on fermentative hydrogen production using canteen based waste under acidophilic microenvironment

Functional role of biomolecules viz., carbohydrates and proteins on acidogenic biohydrogen (H₂) production was studied through the treatment of canteen based composite food waste. The performance was evaluated in an anaerobic sequencing batch reactor (AnSBR) at pH 6 with five variable organic loading conditions (OLR1, 0.854; OLR2, 1.69; OLR3, 3.38; OLR4, 6.54 and OLR5, 9.85 kg COD/m³-day). Experimental data depicted the feasibility of H₂ production from the stabilization of food waste and was found to depend on the substrate load. Among the five loading conditions studied, OLR4 documented maximum H₂ production (69.95 mmol), while higher substrate degradation (3.99 kg COD/m³-day) was observed with OLR5. Specific hydrogen yield (SHY) vary with the removal of different biomolecules and was found to decrease with increase in the OLR. Maximum SHY was observed with hexose removal at OLR1 (139.24 mol/kg Hexose_R at 24 h), followed by pentoses (OLR1, 108.26 mol/kg Pentose_R at 48 h), proteins (OLR1, 109.71 mol/kg Protein_R at 48 h) and total carbohydrates (OLR1, 58.31 mol/kg CHO_R at 24 h). Proteins present in wastewater helped to maintain the buffering capacity but also enhanced the H₂ production by supplying readily available organic nitrogen to the consortia. Along with carbohydrates and proteins, total solids also registered good removal.     

Enhanced methane and hydrogen production from municipal solid waste and agro-industrial by-products co-digested with crude glycerol

The effects of crude glycerol on the performance of single-stage anaerobic reactors treating different types of organic waste were examined. A reactor treating the organic fraction of municipal solid waste produced 1400 mL CH₄/d before the addition of glycerol and 2094 mL CH₄/d after the addition of glycerol. An enhanced methane production rate was also observed when a 1:4 mixture of olive mill wastewater and slaughterhouse wastewater was supplemented with crude glycerol. Specifically, by adding 1% v/v crude glycerol to the feed, the methane production rate increased from 479 mL/d to 1210 mL/d. The extra glycerol-COD added to the feed did not have a negative effect on the reactor performance in either case. Supplementation of the feed with crude glycerol also had a significant positive effect on anaerobic fermentation reactors. Hydrogen yield was 26 mmole H₂/g VS added and 15 mmole H₂/g VS added in a reactor treating the organic fraction of municipal solid waste and a 1:4 mixture of olive mill and slaughterhouse wastewater. The addition of crude glycerol to the feed enhanced hydrogen yield at 2.9 mmole H₂/g glycerol added and 0.7 mmole H₂/g glycerol added.     

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.     

甘薯淀粉废水发酵生产微生物油脂的研究

研究了废水预处理方式及添加营养因子对产油菌株FR在甘薯淀粉废水中生长、产油及COD去除的影响。发现不经稀释的废水发酵效果优于稀释后的效果,采用淀粉酶液化处理、添加碳氮比、添加Mn2 均能够促进菌株FR生长、产油和COD去除,淀粉酶液化处理后的产油率可达45.3%,淀粉酶和糖化酶先后处理后的COD去除率可达66.3%。Mg2 的加入可以提高生物量。     

Laboratory scale examination of the effects of overloading on the anaerobic digestion by glycerol

The anaerobic digestion of pure glycerol, which produces a baseline acetic acid to propionic acid ratio of 0.2, was studied in laboratory scale reactors (3 l working volume) at mesophilic temperature (37 °C) with 3000 mg chemical oxygen demand (COD) l⁻¹d⁻¹. During the experiment tVFA and C2-C6 VFA analysis and daily biogas yield measurement were carried out. Following 10 days of a 15% d⁻¹ increase in the organic loading rate (OLR) of 3.0-10.5 g COD l⁻¹d⁻¹, the concentration of propionic acid increased to 6200-8000 mg l⁻¹. Then the inoculum was divided into three parts feeding with 100% glycerol, 50% glycerol + 50% acetic acid, and 50% glycerol + 50% thick stillage, (presented in % of 2.60 g COD l⁻¹d⁻¹ OLR), respectively. The application of co-substrates reduced the recovery period by 5 days compared to feeding with pure glycerol. When the reactors were loaded with glycerol again (10% OLR raise per day) the previously applied co-substrates had a positive effect on the VFA composition and the biogas yield as well.     

Production of microbial lipid by Cryptococcus curvatus on rice straw hydrolysates

Microbial biolipids/biodiesels derived from volatile fatty acids (VFAs) can be a valuable alternative to plant oils if optimum fermentation conditions are determined. VFAs were used for cell mass and microbial lipid production by Cryptococcus curvatus. The lipid content in the cells increased up to 48% and 28% in batch cultures with the use of 20 g/L glucose and 6 g/L of VFAs as the carbon source, respectively. In this study, C. curvatus used VFAs as a carbon source via anaerobic digestion of rice straw hydrolysates. VFAs produced from rice straw resulted in yield of 0.43 g VFAs/g substrate and 40% higher specific growth rate(0.305 h⁻¹) than synthetic VFAs. The highest fatty acid composition observed was C18:1, was obtained using glucose and VFAs as the carbon source to yield a cetane number of 56–59, which is suitable for biodiesel production. The cost of microbial lipids was estimated to be 0.30–1.15 USD/L given 0–150 USD/ton of VFAs cost for a yield of 0.17 g/g of lipids. Thus, VFAs can be a suitable carbon source for economical biodiesel production.     

Anaerobic co-digestion of food waste and piggery wastewater: focusing on the role of trace elements

The objective of this study was to evaluate the feasibility of anaerobic co-digestion of food waste and piggery wastewater, and to identify the key factors governing the co-digestion performance. The analytical results indicated that the food waste contained higher energy potential and lower concentrations of trace elements than the piggery wastewater. Anaerobic co-digestion showed a significantly improved biogas productivity and process stability. The results of co-digestion of the food waste with the different fractions of the piggery wastewater suggested that trace element might be the reason for enhancing the co-digestion performance. By supplementing the trace elements, a long-term anaerobic digestion of the food waste only resulted in a high methane yield of 0.396 m³/kg VS_added and 75.6% of VS destruction with no significant volatile fatty acid accumulation. These results suggested that the typical Korean food waste was deficient with some trace elements required for anaerobic digestion.     

Anaerobic hydrolysis and acidification of organic substrates: determination of anaerobic hydrolytic potential

This study aimed to develop a biochemical-test mainly to evaluate the hydrolytic-potential of different substrates and to apply this test to characterize various organic substrates. Outcome of this study can be used for optimization of the WWTPs through enhancement of N/P removal or anaerobic digestion. Out of four series of batch experiments, the first two tests were conducted to determine the optimal operating conditions (test duration, inoculum-ratio etc.) for the hydrolytic-potential test using secondary and synthetically-prepared sludges. Based on the results (generation of CODs, pH and VFA), test duration was fixed between 6 and 7 d allowing to attain maximum hydrolysis and to avoid methanogenesis. Effect of inoculum-ratios on acid fermentation of sludge was not significantly noticed. Using this methodology, third and fourth tests were performed to characterize various organic substrates namely secondary, pre-treated sludge, pig and two different cattle slurries. VFA production was shown to be substantially dependent on substrates types.     

餐厨垃圾协同剩余污泥发酵产酸的生物过程与影响因素研究进展

资源化利用是应对餐厨垃圾(Kitchen waste,KW)和剩余污泥(Excess sludge,ES)快速增加的有效方法,而厌氧发酵获得挥发性脂肪酸(Volatile fatty acids,VFAs)是其中的重要方式之一,但单一底物限制了VFAs的高效生产.近年来,不同底物厌氧共发酵产生VFAs被广泛研究与应用,...     

A pilot scale two-stage anaerobic digester treating food waste leachate (FWL): Performance and microbial structure analysis using pyrosequencing

Food waste leachate (FWL) from the food waste recycling facilities in Korea is a serious environmental problem. Much research was done on anaerobic digestion of FWL in a lab-scale; however, there is little information on a large scale anaerobic digestion system (ADS). In this study, a two-phase ADS in a pilot scale was operated using FWL and the ADS performance and microbial structure dynamics using pyrosequencing were investigated. The ADS was operated for 136 days using FWL containing a high concentration of volatile fatty acid (12,435 ± 2203 mg/L), exhibiting volatile acid (VS) removal efficiency of 74–89% and CH₄ yield of 0.39–0.85 Nm³/kg of reduced VS. The microbial structure at 76, 101, and 132 days indicated the methanogen population shift from acetoclastic methanogens (Methanosarcina and Methanosaeta) to hydrogenotrophic methanogens (Methanobacterium and Methanoculleus). The bacterial community also shifted to the taxa syntrophically related with hydrogenotrophic methanogens (Clostridia). The statistical analysis revealed the positive correlation of VS removal efficiency with Methanosarcina, but the negative correlation with Methanobacterium. The results presented here suggest that acetoclastic methanogens and their associated bacteria were more efficient for VS removal in the pilot scale ADS system, providing useful information for FWL treatment in a large scale ADS.     

Buffer requirements for enhanced hydrogen production in acidogenic digestion of food wastes

The requirements for pH buffer addition for hydrogen production and acidogenesis in batch acidogenic digestion of a food waste (FW) feedstock with limited alkalinity was studied at various initial pH conditions (6.0–8.0). The results showed that, without buffer addition, hydrogen production from this feedstock was insignificant regardless of the initial pH. With buffer addition, hydrogen production improved significantly if the initial pH was greater than 6.0. Substantial hydrogen production occurred when the pH at the end of the batch digestion was higher than 5.5. The maximum hydrogen production was found to be 120 mL/g VS added when the initial pH was 6.5 and buffer addition was in the range of 15–20 mmol/g VS. The effect of pH buffering on the formation of volatile fatty acids (acetic acid, propionic acid and butyric acid) was similar to its effect on hydrogen production. The results of this study clearly indicated shifts in the metabolic pathways with the pH of fermentation. The changes in metabolic pathways impacted upon the dosage of buffer that was required to achieve maximum hydrogen generation.