Higher Volatile Fatty Acids Research Articles

Biostimulation of sewage sludge solubilization and methanization by hyper-thermophilic pre-hydrolysis stage and the shifts of microbial structure profiles

This study evaluated the influence of hyper-thermophilic pre-hydrolysis stage (70 °C) on methane recovery of sewage sludge at 35 °C. In this configuration, the process performance in both temperatures were estimated and the microbial communities were characterized by full-length16S rRNA genes and/or microbial activities. In addition, the appropriate solubilization reaction time was assessed. The results revealed that the higher hydrolysis and acidogenesis activities were achieved with longer reaction time of pretreatment (5 days) and thus higher organic nitrogen conversion and alkalinity were attained. Under appropriate pretreatment reaction time, pretreated sludge was characterized by 65% higher organic matters solubilization and 1.4-fold higher volatile fatty acids (VFAs) concentration compared to raw sludge. The overall methane yield produced under this scenario was 179 L CH4. KgVSin, with 15% of the absolute yield was produced in hydrolysis reactor. 50% reduction in bacteria belong to Firmicurtes was observed at mesophilic reactor and meanwhile the relative abundance of Bacteroidetes and Cloacimonetes were enhanced. The predominant methanogens in both stages did not change implying adaptation of Methanothermobacter (>62%) to mesophilic condition. However, increasing acetoclastic methanogens up to 30% in mesophilic reactor indicating methane was produced from pretreated sludge mainly through H2– mediated CO2 reduction and partially from acetate cleavage. The results highlight the key role of hyper-thermophilic pre-hydrolysis stage for better stabilization of sewage sludge without further investments in current biogas plants.

Carbide slag pretreatment enhances volatile fatty acid production in anaerobic fermentation of four grass biomasses

Anaerobic fermentation of biomasses for volatile fatty acid (VFA) production has attracted widespread attention. Grass biomasses have the advantages of high yield, rapid and perennial growth, low lignin content and low input, etc. In order to improve VFA production from grass biomasses, carbide slag was applied to pretreat four grass biomasses (panicum virgatum, triarrhena lutarioriparia, medicago sativa and turfgrass pruning) before anaerobic fermentation. Results showed that carbide slag pretreatment changed the structure of grass biomasses and enhanced their crystallinity index (CrI). The reducing sugar yield and VFA production from four pretreated grass biomasses were significantly improved. Pretreated turfgrass pruning was the most promising grass compared with other grass biomasses, with the highest VFA production of 8803.87 mg/L and volatile solid removal of 56.76%. Kinetic results indicated that the first order kinetic model, cone model and modified Gompertz model all fitted well with VFA production (R2 > 0.96), and pretreated turfgrass pruning achieved the highest VFA production potential of 11270 mg/L. Turfgrass pruning was the most suitable grass biomass for enzymatic hydrolysis and anaerobic fermentation due to a lower lignin content and CrI. High VS removal revealed that carbide slag pretreatment promoted substrate hydrolysis and further VFA production. There existed a positive correlation between enzymatic hydrolysis and anaerobic fermentation of grass biomasses (R2 = 0.9064). Results of microbial community structure indicated that the high VFA production from turfgrass pruning after carbide slag pretreatment was mainly contributed to enrichment of phylum Firmicutes and genus Clostridium.

Biological pretreatment with Trametes versicolor to enhance methane production from lignocellulosic biomass: A metagenomic approach

The presence of poorly biodegradable components in lignocellulosic biomass limits the methane recovery in anaerobic digesters. The main reason to go for aerobic pretreatment before anaerobic digestion (AD) is to enable enzymatic cleavage of the aromatic rings in lignin by oxygen since it cannot be efficiently degraded under anaerobic conditions. In this study, the advantage of highly-cellulolytic white-rot fungi Trametes versicolor was taken by aerobic pretreatment prior to anaerobic co-digestion of cow manure and selected cereal crop materials (i.e. wheat, rye, barley, triticale) harvested at different stages. Fungal pretreatment improved the methane yield by 10%–18% and cellulose degradation up to 80%. Furthermore, higher volatile fatty acid (VFA) speciation was found in the anaerobic digesters upon fungal pretreatment. 16S rRNA gene amplicon sequencing revealed a more diverse microbial community in the fungal-pretreated anaerobic digesters. Generally, typically-detected bacterial species dominated the digesters; except that Synergistetes was only enriched in the fungal-pretreated digesters. Although Methanosarcianease was the predominant methanogenic archaea, a more diverse methanogenic population was identified in the fungal-pretreated digesters in which Methanobacteriaceaa and Methanomibrobiaceae also took role during biomethanation. Comparatively more unique microbiome of biogas reactors upon fungal pretreatment synergistically affected VFA production, cellulose degradation and eventually methane yield in an affirmative way. Considering the functional importance of bacterial and methanogenic archaeal populations, elevated knowledge of the microbial structures is essential for minimizing process failures and for creating strategies for process optimization of lignocellulose based-AD.

Effect of hydrothermal pretreatment severity on the pretreatment characteristics and anaerobic digestion performance of corn stover

The pretreatment characteristics and anaerobic digestion (AD) performance of corn stover were investigated at different hydrothermal pretreatment (HP) severity levels. The pretreatment of corn stover with and without ammonia was performed at different temperatures (100, 150, and 200 °C) and with a holding time of 5–30 mins. Results showed that after HP, the highest volatile fatty acid (VFAs) concentration was 10533.94 mg/L at a HP severity of 7.27, which was 1.72–3.35 times greater than those of others HP severity levels. Similarly, the highest removal rates of hemicellulose and lignin were 95.41% and 13.85% for HP severity levels of 6.81 and 1.98, respectively. The maximum biogas and methane increasing yield at 100 °C holding 30 min without ammonia were 16.26% and 22.74% greater than that of the untreated, respectively. These results suggest that an appropriate HP intensity can promote biogas production.

The effect of acidogenic and methanogenic conditions on the availability and stability of carbon, nitrogen and phosphorus in a digestate

Acidification and drying of digestate are important post-treatment for, respectively, improving nutrient availability and hygiene. These approaches are expected to reduce digestate soil application mass and increase its value. This study compared eleven organic feedstocks under acidogenic and methanogenic conditions as a sustainable approach to improving phosphorus availablity, organic carbon and stabilising ammoniacal nitrogen of the resulting digestate under thermal drying. The result showed increases in phosphate concentration under acidogenic conditions and reduction in ammonium nitrogen after drying at 100 °C. The highest phosphate values of 3.2 ± 0.38 g/kg were achieved using whey permeate substrate while the effect of drying on ammonium nitrogen concentration was lowest for acidogenic bird seed fermentation with an ammonium loss of 59.7%. Both results were facilitated by high total volatile fatty acid concentration produced from available organic carbon which reached a maximum value of 5.71 ± 0.53 g/L, respectively. Increases in phosphate and ammonium nitrogen stability under acidogenic conditions was a consequence of lower pH, a condition synonymous with acidogenic only fermentation. The accumulated volatile fatty acid contributed to higher carbon to nitrogen ratio under acidogenic fermentation. Higher labile carbon to nitrogen ratio can trigger immobilization of ammonium nitrogen in the soil and this presents a case for subsequent experimentation into acidogenic digestate application in soil.

The use of sugar beet pulp stillage for co-digestion with sewage sludge and poultry manure.

The anaerobic mesophilic co-digestion of sugar beet pulp stillage with poultry manure and municipal sewage sludge was investigated in this study. The sugar beet pulp stillage (SBPS) mono-digestion failed owing to an accumulation of volatile fatty acids, leading to a pH value lower than 5.5. A 20% addition of poultry manure to stillage allowed for stable digestion performance despite high volatile fatty acid (total volatile fatty acids) concentrations of 5500-8500 g m-3 with propionic acid being the predominant one and constituting 72%-76% total volatile fatty acids. For this mixture, the maximum methane production of 418 dm3 kgVSfed-1 was achieved when the reactor was operated at a solids retention time of 20 days and an organic loading rate of 4.25 kgVS m-3 d-1. The co-digestion of stillage with 60% municipal sewage sludge gave the average methane yield of around 357 dm3 kgVSfed-1 for all operational conditions applied, however, the methane percentage of biogas (up to 70%) was far greater than the corresponding values obtained for sugar beet pulp stillage-poultry manure co-digestion. Neither ammonia nor volatile fatty acids destabilised the biogas production, and the volatile fatty acid profile showed the dominance of acetic acid (72%-82% total volatile fatty acids) followed by propionic and butyric acids.

A comparative study of biogasification of wheat straw, sugarcane bagasse and pressmud

A study to compare biogas production potentials of wheat straw, sugarcane bagasse and pressmud was conducted at pH 8.0, temperature 40 °C and substrate concentration 20 g/L. Raw substrates were thermogravimetrically and Fourier-transform infrared spectroscopically characterised. TGA showed the weight loss of samples attributable to moisture, hemicellulose, cellulose and lignin losses. FTIR analysis indicated functional groups characteristics of hemicellulose, cellulose and lignin. Biogas production was the maximum between 10th and 25th day for all the tests. WS with 10% inoculum showed the highest cumulative biogas production of 370 mL/g followed by the SB (316 mL/g) and PM (211 mL/g) counterparts. The corresponding values with 5% inoculum were 303 mL/g (WS), 244 mL/g (SB) and 152 mL/g (PM). The inoculum volume also positively affected the cumulative biogas production (22.1, 29.5 and 38.8% respectively). The higher volatile fatty acids as observed in case of WS which further facilitated higher biogas production could be due to its maximum volatile solids content (88.9%) and water swelling capacity (7.37). A consistently increasing trend in the methane content (varying between 54 and 61%) in all the tests was observed till the 20th day. The biogas (7.7–21.7 mL/g) and the methane (35–42%) contents showed a decreasing trend thereafter, the lowest being observed during the 35–40-day period.

Acidogenic properties of carbohydrate-rich wasted potato and microbial community analysis: Effect of pH

Vegetable waste is one of the major organic solid residues available for sustainable biogas production. The aim of this study was to investigate the possibility and optimal controlling strategy for acidogenic fermentation of wasted potato (WP). Three leaching bed reactors (LBRs) were operated at various pH values (6.0, 7.0 and 8.0) with an organic loading rate (OLR) of 6.7g volatile solid/(L·d) and hydraulic retention time of 6d. Butyric acid-type fermentation with butyric acid as predominant volatile fatty acid (VFA) was observed with a concentration and proportion (of total VFAs) of butyric acid, which were 7.8g/L, 49.7 % and 9.6g/L and 52.2 % at pH 6.0 and 7.0, respectively. Conversely, at pH 8.0, mixed acid-type fermentation was observed with acetic and butyric acid as the major VFAs. Control experiment without pH manipulation didn't perform well in VFAs production at first 6 days and then VFAs concentration increased as pH value was adjusted to 8. It was indicated that the inhibition was caused by high undissociated VFAs concentration due to low pH and the VFAs production could be improved through pH control strategy to regulate the undissociated VFAs concentration. According to the bacterial analysis, the microbial community was diverse and Firmicutes were the most important bacteria at different pH conditions. Therefore, the results suggested that a process of pH control might be feasible for stable and efficient acidogenic fermentation.

Nutrient composition and in vitro fermentability of corn grain and stover harvested at different periods in Goesan, a mountainous area.

With South Korea’s limited capability of feed production because of its relatively small cultivable area, the country is pushed to depend on foreign feed imports despite the immensely fluctuating price of corn. Hence, intensive efforts to increase the total cultivable area in Korea like extending of farming to mountainous area is being practiced. Corn was planted in Goesan County, a mountainous area in the country. Grain and stover were harvested separately in three harvest periods: early-harvest (Aug 8), mid-harvest (Aug 18), and late-harvest (Aug 28). The nutrient composition such as dry matter (DM), crude protein (CP), crude fat (EE), organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF), and non-fibrous carbohydrates (NFC) was determined after harvest. Effective degradability (ED) of the major nutrients (DM, NDF, ADF, and CP) were measured through in vitro fermentation of rumen fluid from Hanwoo (Korean cattle). pH, ammonia-N concentration, volatile fatty acid (VFA) concentration, and gas production were periodically measured at 0, 3, 6, 12, 24, 48, and 72 h. Corn grain showed higher nutrient content and ED than stover. It also had higher gas production but its pH, ammonia-N, and total VFA concentration were lower than corn stover. The best nutrient composition of corn grain was observed in early-harvest (high CP, EE, NDF, OM, NFC, and low ADF). Early-harvest of corn grain also had high effective degradability of dry matter (EDDM), effective degradability of neutral detergent fiber (EDNDF), effective degradability of acid detergent fiber (EDADF), and total VFA concentration. On the other hand, the best nutrient composition of stover was observed in mid-harvest (high DM, CP, NDF, and low ADF). EDDM, EDNDF, and EDADF were pronounced in early-harvest and mid-harvest of stover but the latter showed high total VFA concentration. Hence, early and mid-harvested corn stover and grain in a mountainous area preserved their nutrients, which led to the effective degradation of major nutrients and high VFA production.

An integrated approach for waste activated sludge management towards electric energy production/resource reuse

This study developed an integrated approach for electric energy harvest/resource reuse from waste activated sludge (WAS) pretreated by enzymolysis based on anaerobic fermentation and microbial fuel cells (MFCs). WAS solubilization by the 3-h enzymatic pretreatment (a blend of hydrolytic enzymes caused over 5300 mg/L soluble COD release) prompted volatile fatty acid (VFA) production with 3580 mg COD/L after 10-d fermentation. After solid-liquid separation, fermentation liquid with high VFA content was fed into MFCs for electric energy production, while solid residues were used for making building materials (such as blended cements). Results showed that the electricity conversion efficiency of fermentation liquid (VFA) reached 1.254 kW h/kg COD with over 90% organics removal and solid residues could be consumed potentially as qualified substitutes for producing cements. As such, this study may provide some new thinking on future WAS management towards electricity harvest/resource reuse with zero secondary wastes discharge.

Inactivation of Salmonella during dry co-digestion of food waste and pig manure

Extremely high volatile fatty acids (VFAs) and ammonia concentrations can accumulate during dry co-digestion of organic wastes, which may inactivate pathogenic microorganisms. In this study, inactivation of Salmonella during dry co-digestion of pig manure (PM) and food waste (FW), which are both reservoirs of zoonotic pathogens, was examined. The effects of pH, VFAs, ammonia and their interactions were assessed on three inoculated Salmonella serotypes. The results show that dry co-digestion significantly decreased the Salmonella inactivation time from several months (in wet digestion) to as short as 6–7 days. A modified Weibull distribution was proposed to simulate Salmonella reduction and to calculate or predict the minimum inhibitory concentrations (MIC) of VFAs and ammonia. Statistical analysis showed that all the factors (pH, VFA type, VFA/ammonia concentration and Salmonella serotype) significantly impacted Salmonella inactivation (P < 0.01). The inhibitory effect sequence was pH > VFA concentration > VFA type > Salmonella serotype in VFA MIC tests, and ammonia concentration > pH > Salmonella serotype in ammonia MIC tests. The toxicity of VFAs was much greater than that of ammonia, and an antagonistic effect was found between VFAs and ammonia on Salmonella inactivation. Apart from the toxicity of free VFAs and free ammonia, the inhibitory effects of pH alone, ionized VFAs and ammonium were also observed.

Synergistic effects of iron and persulfate on the efficient production of volatile fatty acids from waste activated sludge: Understanding the roles of bioavailable substrates, microbial community & activities, and environmental factors

Evident synergistic effects of iron activated persulfate (Fe/PS) on the marked promotion of volatile fatty acids (VFAs) from waste activated sludge during anaerobic fermentation were reported. The maximal VFAs concentration was up to 2255 mg COD/L with the proportion of 72.8% acetic acid in the Fe/PS reactor while it was merely 120 and 517 mg COD/L in Fe and PS reactors, respectively. Fe/PS treatment could substantially improve the solubilization and hydrolysis processes via the combined chemical and biologic effects to provide sufficient bioavailable substrates for acidogenic bacteria. Meanwhile, the presence of Fe in Fe/PS reactors could alleviate the adverse effects of PS on environmental factors (i.e. ORP and pH) and simultaneously involve in the regulation of microbial growth and activities. The fermentative bacteria responsible for VFAs production were highly enriched and the activities of key acid-forming enzymes and ATP concentration were greatly improved in Fe/PS reactors. It was the overall improvement of bioavailable substrates, abundance and activities of acidogenic bacteria, and fermentation conditions that led to the high VFAs accumulation in Fe/PS reactors.

Effect of inoculum and substrate/inoculum ratio on the performance and methanogenic archaeal community structure in solid state anaerobic co-digestion of tomato residues with dairy manure and corn stover

Effects of methanogenic community of inoculum (liquid anaerobic digestion effluent (L-AD effluent), waste activated sludge (WAS), and anaerobic granular sludge (AGS)) and substrate/inoculum ratio (S/I) on reactor performance in solid state anaerobic digestion (SS-AD) were investigated. L-AD effluent, which can provide sufficient microbes and enough buffering capacity to the reactor at an S/I ratio of 6, was found to quickly initiate SS-AD processes. The highest methane production was obtained in reactor inoculated with WAS at an S/I ratio of 2. Higher volatile fatty acids and total ammonia nitrogen concentrations were found when AGS was used as inoculum, which led to a low methane production. Methanosaetaceae, Methanosaetaceae, and Methanosaetaceae together with Methanobacteriaceae were the dominant methanogens in reactors inoculated with L-AD effluent, WAS, and AGS, respectively. These findings suggest among the three inoculum, L-AD effluent is the most effective inoculum for SS-AD of on farm organic waste.

Volatile fatty acids (VFAs) and methane from food waste and cow slurry: Comparison of biogas and VFA fermentation processes

AbstractThe potential of various biomasses for the production of green chemicals is currently one of the key topics in the field of the circular economy. Volatile fatty acids (VFAs) are intermediates in the methane formation pathway of anaerobic digestion and they can be produced in similar reactors as biogas to increase the productivity of a digestion plant, as VFAs have more varying end uses compared to biogas and methane. In this study, the aim was to assess the biogas and VFA production of food waste (FW) and cow slurry (CS) using the anaerobic biogas plant inoculum treating the corresponding substrates. The biogas and VFA production of both biomasses were studied in identical batch scale laboratory conditions while the process performance was assessed with chemical and microbial analyses. As a result, FW and CS were shown to have different chemical performances and microbial dynamics in both VFA and biogas processes. FW as a substrate showed higher yields in both processes (435 ml CH4/g VSfed and 434 mg VFA/g VSfed) due to its characteristics (pH, organic composition, microbial communities), and thus, the vast volume of CS makes it also a relevant substrate for VFA and biogas production. In this study, VFA profiles were highly dependent on the substrate and inoculum characteristics, while orders Clostridiales and Lactobacillales were connected with high VFA and butyric acid production with FW as a substrate. In conclusion, anaerobic digestion supports the implementation of the waste management hierarchy as it enables the production of renewable green chemicals from both urban and rural waste materials.

Cost-effective, low thermo-chemo disperser pretreatment for biogas production potential of marine macroalgae Chaetomorpha antennina

In this study, a novel attempt has been made to generate energy-efficient biomethane from marine macroalgae (Chaetomorpha antennina) by coupling thermochemical liquefaction with a disperser (thermo-chemo disperser (TCD) liquefaction). A temperature of (80 °C), pH 11 and disperser g-force of 1613 g were considered optimal parameters for effective solubilization and energy-efficient methane generation. This combinative liquefaction considerably reduced the treatment time and specific energy from 60 to 15 min and 6294 to 800 kJ/kg TS. The highest volatile fatty acids (VFA) accumulation of 890 mg/L was recorded in TCD compared to a thermo disperser (TD) (750 mg/L) and disperser (D) (322 mg/L) during anaerobic fermentation. TCD enhances the methane production potential of macroalgal biomass and a higher methane production of 215 mL/g VS was achieved for TCD compared to TD (149 mL/g VS) and D samples (100 mL/g VS), respectively. Cost analysis confirmed the field applicability of TCD liquefaction with a net profit of 90 USD/ton of marine macroalgae. A high energy ratio of 1.5 was achieved with the proposed mode of pretreatment (TCD) compared to TD (0.95) and D (0.28) pretreatment. Therefore, C. antennina is considered a suitable feedstock for methane generation.

Inhibition of volatile fatty acids on methane production kinetics during dry co-digestion of food waste and pig manure

Compared with wet digestion, dry digestion of organic wastes reduces reactor volume and requires less energy for heating, but it is easily inhibited by high volatile fatty acid (VFA) or ammonia concentration. The inhibition on methane production kinetics during dry co-digestion of food waste and pig manure is rarely reported. The aim of this study was to explore the inhibition mechanisms and the microbial interactions in food waste and pig manure dry co-digestion systems at different inoculum rates (25% and 50% based on volatile solids) and food waste/pig manure ratios (0:100, 25:75, 50:50, 75:25 and 100:0 based on volatile solids). The results showed that the preferable operation conditions were obtained at the inoculum rate of 50% and food waste/pig manure ratio of 50:50, with a specific methane yield of 263 mL/g VSadded. High VFA concentration was the main inhibition factor on methane production, and the threshold VFA inhibition concentrations ranged 16.5–18.0 g/L. Syntrophic oxidation with hydrogenotrophic methanogenesis might be the main methane production pathway in dry co-digestion systems due to the dominance of hydrogenotrophic methanogens in the archaeal community. In conclusion, dry co-digestion of food waste and pig manure is feasible for methane production without pH adjustment and can be operated stably by choosing proper operation conditions.

Enhanced PHA Production with Mixed Cultures Using a Robust and Simple Controller

This work proposes the use of feedback control tools to enhance the production of bacterial polyhydroxyalkanoates (PHA) in an aerobic bioreactor fed with volatile fatty acids (VFA), by regulating the dissolved oxygen (DO) concentration at an optimal reference value and using the airflow signal behaviour to decide when to stop the reaction. The proposed method uses a standard proportional-integral (PI) controller to regulate the DO at a reference value by modifying the airflow, and this latter signal as an indicator to stop the reaction. Experiments were carried out in a batch aerobic bioreactor inoculated with enriched PHA-producing biomass from another bioreactor to determine the optimal DO reference value for PHA production and to compare the proposed operational scheme with the usual strategy that uses a constant airflow. The proposed method allows operation at a DO set-point that is optimal for PHA production and is able to identify the total degradation of substrate by a simple algorithm. It can cope with high VFA influent concentrations and inhibition because of PHA accumulation, by adapting the reaction time on-line. The PHA productivity rate was enhanced and the air consumption was decreased when compared with the usual operation strategy for this type of system. The method is able to identify the end of the reaction using the online measured airflow signal, enhances PHA production, improves the substrate rate and saves air consumption.

Simultaneous biogas upgrading and biochemicals production using anaerobic bacterial mixed cultures

A novel biological process to upgrade biogas was developed and optimised during the current study. In this process, CO2 in the biogas and externally provided H2 were fermented under mesophilic conditions to volatile fatty acids (VFAs), which are building blocks of higher-value biofuels. Meanwhile, the biogas was upgraded to biomethane (CH4 >95%), which can be used as a vehicle fuel or injected into the natural gas grid. To establish an efficient fermentative microbial platform, a thermal (at two different temperatures of 70 °C and 90 °C) and a chemical pretreatment method using 2-bromoethanesulfonate were investigated initially to inhibit methanogenesis and enrich the acetogenic bacterial inoculum. Subsequently, the effect of different H2:CO2 ratios on the efficiency of biogas upgrading and production of VFAs were further explored. The composition of the microbial community under different treatment methods and gas ratios has also been unravelled using 16S rRNA analysis. The chemical treatment of the inoculum had successfully blocked the activity of methanogens and enhanced the VFAs production, especially acetate. The chemical treatment led to a significantly better acetate production (291 mg HAc/L) compared to the thermal treatment. Based upon 16S rRNA gene sequencing, it was found that H2-utilizing methanogens were the dominant species in the thermally treated inoculum, while a significantly lower abundance of methanogens was observed in the chemically treated inoculum. The highest biogas content (96% (v/v)) and acetate production were achieved for 2H2:1CO2 ratio (v/v), with Acetoanaerobium noterae, as the dominant homoacetogenic hydrogen scavenger. Results from the present study can pave the way towards more development with respect to microorganisms and conditions for high efficient VFAs production and biogas upgrading.

Influence of sulfuric acid concentration on biohydrogen production from rice mill wastewater using pure and coculture of Enterobacter aerogenes and Citrobacter freundii

We report a concise study on the influence of sulfuric acid concentration used in the hydrolysis of rice mill wastewater on biohydrogen production using pure as well as co-culture of Enterobacter aerogenes and Citrobacter freundii. A higher total reducing sugar release of 14.2 g/L was obtained with 1.5% sulfuric acid (v/v). The effect of pH on cumulative biohydrogen production from 1.5% acid hydrolyzed rice mill wastewater was investigated using pure and coculture of Enterobacter aerogenes and Citrobacter ferundii. The fermentative hydrogen production using mixed culture showed a maximum hydrogen yield of 1.61 mol/mol sugar. In addition, about 70% reduction in chemical oxygen demand (COD) and higher volatile fatty acids (VFA) production were observed. Modified Logistic, Gompertz and Richards models were used to fit cumulative hydrogen production data whereas Logistic equation was used fit growth data. Richards model showed best fit and Logistic equation gave least error in predicting maximum hydrogen producing potential.

Build-up and impact of volatile fatty acids on E. coli and A. lumbricoides during co-digestion of urine diverting dehydrating toilet (UDDT-F) faeces

This study examined the potential of Escherichia coli (E. coli) and Ascaris lumbricoides (A. lumbricoides) eggs inactivation in faecal matter coming from urine diverting dehydrating toilets (UDDT-F) by applying high concentrations of volatile fatty acids (VFAs) during anaerobic stabilization. The impact of individual VFAs on E. coli and A. lumbricoides eggs inactivation in UDDT-F was assessed by applying various concentrations of store-bought acetate, propionate and butyrate. High VFA concentrations were also obtained by performing co-digestion of UDDT-F with organic market waste (OMW) using various mixing ratios. All experiments were performed under anaerobic conditions in laboratory scale batch assays at 35±1 °C.A correlation was observed between E. coli log inactivation and VFA concentration. Store bought VFA spiked UDDT-F substrates achieved E. coli inactivation up to 4.7 log units/day compared to UDDT-F control sample that achieved 0.6 log units/day. In co-digesting UDDT-F and organic market waste (OMW), a ND-VFA concentration of 4800–6000 mg/L was needed to achieve E. coli log inactivation to below detectable levels and complete A. lumbricoides egg inactivation in less than four days. E. coli and A. lumbricoides egg inactivation was found to be related to the concentration of non-dissociated VFA (ND-VFA), increasing with an increase in the OMW fraction in the feed substrate. Highest ND-VFA concentration of 6500 mg/L was obtained at a UDDT-F:OMW ratio 1:1, below which there was a decline, attributed to product inhibition of acidogenic bacteria. Results of our present research showed the potential for E. coli and A. lumbricoides inactivation from UDDT-F up to WHO standards by allowing VFA build-up during anaerobic stabilization of faecal matter.