Anaerobic co-digestion of chicken litter with food and agro-industrial wastes/residues, an Australian case study: use of carbon-to-nitrogen ratio for substrate mixing and semi-solids versus wet anaerobic digestion

In Victoria, Australia, around 0.45 million tonnes of chicken litter (CL) are produced every year. CL has high potential for bioenergy production, mainly in the form of biogas (methane), however, it has not been widely practiced because it has high levels of protein and uric acid which are known to cause inhibition, during anaerobic digestion (AD), in the form of ammonia. The current CL management practice is to transport CL to a composting facility which has limited benefit to the broiler industries. This has triggered research to assess the feasibility of biogas production from broiler farms¿ CL co-digested with other substrates. Among the agro-industrial wastes usually available in the proximity of chicken farms are agro-industry processing wastes and agricultural residues such as yoghurt whey (YW), wheat straw (WS) and hay grass (HG). Municipal waste i.e. the food wastes (FW) in the household bins is also available to use. These wastes have high methane potential; but varying characteristics and composition, e.g. carbon-to-nitrogen (C/N) ratio, pH, alkalinity, ammonia, structural recalcitrance.  Therefore, these wastes need to be characterised, require understanding if they are suitable for co-digestion and what ratios they can be mixed together. Also, most of the literature concerning co-digestion of different wastes focused on mixing one or two wastes; but little research has been done on the co-digestion of a wide variety of solid waste streams. Therefore, an efficient and economic energy recovery from those wastes through anaerobic co-digestion, an investigation into optimum process conditions is required. Wet anaerobic digestion (W-AD) is a well-established technology operating at solids concentration of<10% total solids (TS), whereas, high solids AD (HS-AD), (10-15% TS) and dry AD (D-AD), <15% TS) are not a common practice. This is due to long retention times and types of infrastructure required, but the most important factors are the lack of knowledge concerning treatment operating conditions, loading and composition. However, as most of the agro-industrial wastes have high TS, the research has focused on both conventional wet and high solids AD. The aims of this research are  to assess the potential of anaerobic co-digestion (ACoD) of CL and co-substrates and to determine the optimum AD process  conditions where the process is stabilised and show no inhibition, for different AD configurations, and to assess  the performance of HS-AD and W-AD fed with a range of co-substrates, under continuous feeding conditions for different organic loading rates (OLRs). The research focused on developing a method that can be used to determine the optimum mixing ratio of agro-industrial wastes of varying characteristics, optimum running conditions for continuous AD, pre-treatment of waste to improve bio-degradation and use of the optimum conditions to develop a high solid AD process. The wastes have been characterised thoroughly before doing their biochemical-methane potential (BMP) under conventional W-AD solids concentrations (2-4% volatile solids (VS)). Four different kinetic models i.e. the first order kinetic model, modified Gompertz model, transfer function model and the cone model were used to fit the biogas yield of the single substrates and the modified Gompertz model (R2: 0.93-0.99) showed better fit among all the models which explains the variation in lag phase and methane production rate depending upon the substrate characteristics. The second batch of BMP tests assessed the co-digestion of a range of different wastes mixed using C/N ratio as the control parameters. The batch experiments were designed according the response surface model (RSM). All the BMP tests were carried out in batch assays under mesophilic conditions in duplicates with 1:2 g/g VS of substrate to inoculum. Analysis of the BMP results using Matlab indicated that the maximum methane production could be achieved for a feedstock of 30-35% VS of CL and 65-70% VS of agro-industrial waste (i.e. YW, FW, HG and WS) that have a total C/N ratio of 26-27.5. In the second phase of the experimental work, semi-continuous anaerobic co-digestion were performed at 4-6% TS based on the predictions and conditions from the batch assesses to observe process performances. The AD reactors were operated at organic loading rates (OLRs) of 2.0-3.0 g TS/L. d and hydraulic retention time (HRT) of 20 days. The optimum feedstock (substrates mixture) was CL: FW:WS of 60:20:20, where 73%, 167% and 117% increase in total biogas production at OLR of 2.0, 2.5, 3.0 g TS/L. d, respectively, compared to that from CL, was achieved. Principal component analysis (PCA) was applied with the characteristics parameter and 68.1% of data variability was explained with second principal component. During semi-continuous work, a new concept, that C/N ratio and lignocellulosic structure degradation might be related during AD Digestate, is applied and found that carbohydrate degradation i.e. cellulose and water soluble contents plays a major role in explaining the variation in performance and produced biogas for different feedstocks of balanced C/N ratio. As most of the agro-industrial wastes are lignocellulosic in nature which resists biodegradability, therefore, the next phase of experimental work focused on selective fractionation of lignocellulosic biomass using sequential alkaline (AKP) and dilute acid (DAP) pre-treatments to increase biodegradability. NaOH pre-treatment was applied both on CL (as it had included bedding material in it) and WS under independent factors of NaOH concentration (1-5% w/v), reaction time (30-90 min) and temperature (60-120°C), and experiment design using RSM. The optimum conditions were analyses with Minitab and the optimum conditions are NaOH concentration 1% (W/V) for 30 min at 120ºC and NaOH concentration 5% (W/V) for 90 min at 120ºC for AKP of WS and CL, respectively. Sequential DAP with H2SO4 (1%-3% w/v) was applied with the best conditions found for the AKP using RSM 2 with same conditions as AKP i.e. same temperatures and times.  With sequential DAP+AKP, higher removal of lignin and hemicellulose and an increment of 25% in biogas was obtained compared to single pre-treatment. Finally, High solids AD were performed in sequential batch assays to give it enough time to degrade and to observe the long-time process performances. sequential ACoD at 15% TS was performed and reported with the optimum conditions from the batch assays (W-AD) i.e. CL: FW: WS mixed at a ratio of 35:32.5:32.5 to have C/N ratio of 26.5 over 215 days in six cycles. The reactors that were fed with untreated substrates produced 321.6±13.4 mLN biogas/g VSadded, which increased by 88%, when CL and WS were sequentially pre-treated using AKP and DAP. The VS removal in the reactors that received pre-treated substrates showed improved biogas production compared to those that received untreated feedstock. A VS removal of 55% were observed with AKP+DAP pre-treated substrates fed reactors, compared with only 36% VS removal from untreated substrate fed reactors. A reduction in ammonia and cellulose with an increase in water soluble contents was also observed in the reactors that received these pre-treated substrates. Additionally, it was also noted that biogas production using sequential SS-AD at 15% was almost 38% less than W-AD, however this was negated with the pre-treatment of substrates, indicating that co-digestion at high TS of 15% is achievable

Effect of dietary honey on intestinal microflora and toxicity of mycotoxins in mice

BACKGROUND: Bee honey is a functional food which has a unique composition, antimicrobial properties and bifidogenic effect. In order to assess whether honey can inhibit the toxic effect of mycotoxins, the present study was undertaken. METHODS: Production of biomass and toxins by Aspergillus parasiticus and Aspergillus ochraceus were followed in media without and with honey. Although aflatoxins and ochratoxin A. were administrated to male Swiss albino mice up to 1 μg and 10 ng/kg body weight/day respectively. The experimental animals were fed diets without our with 10% honey for two months. The changes in colonic probiotic bacteria, determintal colon enzyme glucuronidases, and genotoxicity were followed. RESULTS: Addition of 32% in its media increased the biomass of A parasiticus, while the biomass of A. ochraceus decreased and Ochratoxin A. was not produced. When the honey was added at the ratio of 32 and 48% in the medium. No relationship was found between mycelium weight and production of mycotoxins. Oral administration of aflatoxins (mixture of B(1), B(2), G(1) and G(2)) and Ochratoxin A. induced structural and numerical chromosomal aberrations in bone marrow and germ cells of male mice, whereas, honey treatment reduced the genotoxicity of mycotoxins. Also both toxins induced histopathological changes in liver and kidney. Feeding on diet supplemented with honey improved the histopathological changes in case of aflatoxin group, but not in the case of ochratoxin A. group (except of kidney in two cases). No significant differences were found in the activity of colon β-glucuronidase between group fed diet with or without honey. On the other hand, the colon bifido bacteria and lactobacilli counts were increased markedly in group receiving diet supplemented with honey. CONCLUSION: Substituting sugars with honey in processed food can inhibit the harmful and genotoxic effects of mycotoxins, and improve the gut microflora

On the typology and the worship status of sacred trees with a special reference to the Middle East

This article contains the reasons for the establishment of sacred trees in Israel based on a field study. It includes 97 interviews with Muslim and Druze informants. While Muslims (Arabs and Bedouins) consider sacred trees especially as an abode of righteous figures' (Wellis') souls or as having a connection to their graves, the Druze relate sacred trees especially to the events or deeds in the lives of prophets and religious leaders. A literary review shows the existence of 24 known reasons for the establishment of sacred trees worldwide, 11 of which are known in Israel one of these is reported here for the first time. We found different trends in monotheistic and polytheistic religions concerning their current worship of sacred trees

Effect of pre-treatment on sequential anaerobic co-digestion of chicken litter with agricultural and food wastes under semi-solid conditions and comparison with wet anaerobic digestion

Sequential co-digestion batch assays were conducted using feedstocks of chicken litter (CL), food waste (FW) and wheat straw (WS) mixed to a C/N ratio of 26.5 and 15% TS. Untreated mixture produced biogas of 321.6 ± 13.4 mL N /g VS added which improved up to 50% when either CL or WS pre-treated substrates were fed. However, when both pre-treated CL and WS were fed, 80% and 88% increase in total biogas were found with associated VS removal of 49% and 55%, respectively, for alkali and sequential acid pre-treatment. Also, reactors received pre-treated substrates showed reduction in ammonia and digestate cellulose fraction with an increase in water soluble contents. Biogas production using sequential AD at 15% was almost 38% less than BMP biogas at 4%, however this was negated with the pre-treatment indicating that co-digestion at high TS of 15% is achievable. Further testing is required to confirm these results under semi-continuous conditions

Anaerobic digestion/co-digestion kinetic potentials of different agro-industrial wastes: A comparative batch study for C/N optimisation

Anaerobic digestion (AD) of different agro-industrial wastes and their co-digestion potential has been exhaustively studied in this research. It explores variation of feedstock characteristics such as biodegradability and methane potential during AD and anaerobic co-digestion (ACoD) of chicken litter (CL) with yoghurt whey (YW), organic fraction of municipal solid waste (OFMSW), hay grass (HG) and wheat straw (WS) under mesophilic conditions. Comparative performance was made at different loading concentrations (2%, 3% and 4% VS) with 1:2g/g VS of substrate to inoculum and carrying C/N ratio. Among different kinetic models, the AD of single substrates showed better fit to the modified Gompertz model (R 2 : 0.93-0.997) indicating variation in lag phase and methane production rate depend on the substrate characteristics. During ACoD, the methane yield improved by 9-85% through the addition of two, three or four substrates due to the synergistic effect asa result of increased biodegradability and optimum conditions (such asC/N ratio). A surface (optimisation) model indicated that maximum methane production can be achieved by blending chicken litter (30-35%) and a (65-70%) mixture of yoghurt whey, hay and wheat straw with aC/N ratio of (26-27.5)

Characterisation of agro-industrial wastes and their anaerobic digestion/ co-digestion kinetic potential: A comparative batch study

This study investigates the anaerobic digestion (AD) of chicken litter and co-digestion with a range of supplementary feedstocks. It explores variation of feedstock characteristics such as biodegradability and methane potential during anaerobic co-digestion (ACoD) of chicken litter (CL) with yoghurt whey (YW), organic fraction of municipal solid waste (OFMSW), hay grass (HG) and wheat straw (WS) under mesophilic conditions. Comparative performance was made at different loading concentrations (2, 3 and 4% VS) with 1:2 g/g VS of substrate to inoculum and carrying C/N ratio. The AD of single substrates showed better fit to the modified Gompertz model (R2: 0.93-0.997) indicating a longer lag phase and lower methane production rate at higher loading. During ACoD, the methane yield was improved by 9-85% by the addition of two, three or four substrates due to the synergistic effect as a result of increased biodegradability and optimum conditions (such as C/N ratio). A surface (optimisation) model indicated that maximum methane production was achieved by blending chicken litter (30-35%) and a (65-70%) mixture of yoghurt whey, hay and wheat straw with a C/N ratio of (26-27.5)

Anaerobic Codigestion of Municipal Wastewater Treatment Plant Sludge with Food Waste: A Case Study

The aim of this study was to assess the effects of the codigestion of food manufacturing and processing wastes (FW) with sewage sludge (SS), that is, municipal wastewater treatment plant primary sludge and waste activated sludge. Bench scale mesophilic anaerobic reactors were fed intermittently with varying ratio of SS and FW and operated at a hydraulic retention time of 20 days and organic loading of 2.0 kg TS/m3·d. The specific biogas production (SBP) increased by 25% to 50% with the addition of 1%–5% FW to SS which is significantly higher than the SBP from SS of 284±9.7 mLN/g VS added. Although the TS, VS, and tCOD removal slightly increased, the biogas yield and methane content improved significantly and no inhibitory effects were observed as indicated by the stable pH throughout the experiment. Metal screening of the digestate suggested the biosolids meet the guidelines for use as a soil conditioner. Batch biochemical methane potential tests at different ratios of SS : FW were used to determine the optimum ratio using surface model analysis. The results showed that up to 47-48% FW can be codigested with SS. Overall these results confirm that codigestion has great potential in improving the methane yield of SS

Semi-continuous anaerobic co-digestion of chicken litter with agricultural and food wastes: A case study on the effect of carbon/nitrogen ratio, substrates mixing ratio and organic loading

In this study, four agro-industrial substrates, chicken litter (CL), food waste (FW), wheat straw (WS) and hay grass (HG) were assessed as feedstock for anaerobic digestion (AD) under semi-continuous conditions at organic loading rates (OLRs) of 2.0-3.0 g TS/L.d and hydraulic retention time (HRT) of 20 days. Six different substrate mixtures were prepared such that the C/N ratio of each was 20 or more. Using principal component analysis 68.1% of data variability was explained. Biogas production from CL, as a single substrate, was 181.3 ± 9.8 mLN biogas/g VSadded at OLR of 2.0 gTS/L.d. The optimum substrates mixture was CL:FW:WS 60:20:20, where 73.0%, 167.2% and 116.9% increase in total biogas production at OLR of 2.0, 2.5, 3.0 gTS/L.d, respectively, compared to that from CL, was obtained. Digestate sequential fractionation revealed carbohydrate degradation is an important factor that can explain the variation in performance and production of biogas for feedstocks of balanced C/N ratio