Simulation and Optimization of Anaerobic Co-Digestion of Food Waste with Palm Oil Mill Effluent for Biogas Production

Food waste (FW) utilized as substrate for anaerobic digestion (AD) to produce biogas is promising. Simultaneously, waste is handled and value-added products such as biogas and fertilizer are produced. Palm oil mill effluent (POME) is used as the co-substrate. This study aims to simulate the complete process flow of anaerobic co-digestion (AcoD), consisting of pre-treatment of feedstock, biogas upgrading, wastewater treatment and sludge dying using SuperPro Designer. Parameters, namely hydraulic retention time (HRT), recycle ratio of sludge, water to FW ratio (kg/kg) and co-substrate to FW ratio (kg/kg), would affect the performance of digester. The optimization of these parameters is performed using Design-Expert software, involving response surface methodology (RSM). The effects on responses such as methane flow, chemical oxygen demand (COD) and volatile solid (VS) removal efficiencies are analyzed. In treating 25,000 kg/h of feed, the optimized values for HRT, recycle ratio, water to feedstock ratio, POME to FW ratio are 37.2 days, 0.381, 0.027 and 0.004, respectively. The methane yield is 0.30 L CH4/g of COD removed, with COD and VS removal efficiencies of 81.5% and 68.9%, respectively. The project is profitable, with a payback period of 6.14 years and net present value (NPV) of $5,680,000. A comprehensive understanding of AD matures it for commercialization purposes.

P12.09 Clinical features and management of normal pressure hydrocephalus associated with non-obstructive vestibular schwannoma

BACKGROUND Some (elderly) patients present a communicating (normal pressure) hydrocephalus (NPH) in association with or secondary to vestibular schwannoma (VS). We aim to investigate the usefulness ventriculo-peritoneal shunt (VPS) without tumor removal. MATERIALS AND METHODS 8 patients aged from 50 to 78 years received both diagnosis of VS (mean maximum diameter 21 mm, range 13–28 mm) and NPH. None presented the classical Hakim’s triad. They presented isolated ataxia with gait impairment and loss of equilibrium. It was hard to distinguish if these symptoms were due to NPH or to VIII cranial nerve compression. They underwent TAP test, through a lumbar puncture with a very slow whithdrawal of at least 30 ml of cerebrospinal fluid (CSF). RESULTS None of the 8 patients presented improvement after lumbar puncture. Despite this, we decided to proceed with VPS in 4 patients because of a high risk of falls.... All these 4 patients showed clinical improvement after VPS.. The VS were treated as follows: 4 surgery, 2 radiosurgery, 2 observation. CONCLUSIONS Although some authors indicate VS removal as the best option to improve also NPH symptoms, some patients present high risk of falls in the presence of a small VS. These clinical features are more likely to be relayed related to NPH instead of VS.. VPS carries lower postoperative risks compared to VS removal. For this reason, VPS has to be considered, even without a positive response to a TAP test, as a good alternative to improve quality of life in patient affected by NPH associated with VS.

Efficiency of integrated electrooxidation and anaerobic digestion of waste activated sludge

Background Most of the organic content of waste activated sludge (WAS) comprises microbial cells hard to degrade, which must be pre-treated for energy recovery by anaerobic digestion (AD). Electrooxidation pre-treatment (EOP) with boron-doped diamond (BDD) electrode have been considered a promising novel technology that increase hydrolysis rate, by the disintegrating cell walls from WAS. Although electrochemical oxidation could efficiently solubilize organic substances of macromolecules, limited reports are available on EOP of WAS for improving AD. In this endeavour, the mathematical optimization study and the energy analysis of the effects of initial total solids concentrations [TS] of WAS and current density (CD) during EOP on the methane production and removal of chemical oxygen demand (COD) and volatile solids (VS) were investigated. Because limited reports are available on EOP of WAS for improving biogas production, it is not well understood; however, it has started to attract interest of scientists and engineers. Results In the present work, the energy recovery as biogas and WAS conversion were comprehensively affected by CD and [TS], in an integrated EOP and AD system. When working with WAS at 3% of [TS] pre-treated at current density of 24.1 mA/cm2, the highest COD and VS removal were achieved, making it possible to obtain the maximum methane (CH4) production of 305 N-L/kg VS and a positive energy balance of 1.67 kWh/kg VS. Therefore, the current densities used in BDD electrode are adequate to produce the strong oxidant (hydroxyl radical, ·OH) on the electrode surface, allow the oxidation of organic compounds that favours the solubilization of particulate matter and VS from WAS. Conclusions The improvement of VS removal and COD solubilization were due to the effects of pre-treatments, which help to break down the microbial cells for faster subsequent degradation; this allows a decomposition reaction that leads to biodegrade more compounds during AD. The balance was positive, suggesting that even without any optimization the energy used as electricity could be recovered from the increased methane production. It is worth noting that this kind of analysis have not been sufficiently studied so far. It is therefore important to understand how operational parameters can influence the pre-treatment and AD performances. The current study highlights that the mathematical optimization and energy analysis can make the whole process more convenient and feasible.

Effectiveness of the pretreatment methods on mesophilic anaerobic co-digestion of fruit, food and vegetable waste

ABSTRACT Pretreatment of the fruit, food and vegetable waste materials could enhance the biogas generation in a shorter time along with waste reduction. The aim of the present work was to assess the effectiveness of alkaline, hydrothermal, thermal and ultrasonication pretreatment of fruit, food, and vegetable waste with cow dung for the mesophilic anaerobic co-digestion. The mesophilic anaerobic co-digestion of fruit food and vegetable waste as single substrate with cow dung were performed in a laboratory scale 1L batch digester for 30 days at 40 ± 2 oC temperature. Obtained result show that pretreatment process has enhanced the biogas and biomethane production by 35 % and 44.4 % with 19.89 % TS and 17.30 % VS removal in case of ultrasonication pretreatment (100.45 ml biogas/gVS and 27.92 ml CH4/gVS,), while slight increase is found with thermal and hydrothermal pretreatment as compared to untreated FFVW. The biogas production is enhanced by 35%, 20.4%, 5%, 6% and biomethane production are enhanced by 44.4%, 22%, 11%, 9.8% in the case of ultrasonication, alkaline, thermal and hydrothermal pretreatment process, respectively. The stable mesophilic anaerobic co-digestion operation was achieved and impacts of the different pretreatment methods on the biogas yield and net energy recovery along with viability of anaerobic co-digestion have been explored.

Metagenomic Study of Bacterial and Archaeal Populations during Anaerobic Digestion of Lignocellulosic Waste in Lab-scale Biogas Reactors

This study evaluated using 16S rDNA gene-based metagenomics technique the populations of bacteria and archaea in digestate samples from lab-scale anaerobic bioreactors digesting pretreated and untreated coconut husk fiber, pineapple floret and banana stem. Result of biodegradability experiment indicated high microbial activity in digestate (biogas slurry), with untreated banana stem having the highest total solids (TS) and volatile solids (VS) removal efficiencies of 78.3 % and 92.9 % respectively. Similarly, all pretreated substrates exhibited higher TS and VS losses with corresponding TS (77.8 %) and VS (87.2 %) removal efficiencies. This TS and VS removal rates signaled increased rate of organic matter decomposition with concomitant biogas productivity. Diversity comparisons performed between samples showed rich microbial diversity in untreated sample than the pretreated sample. Taxonomic composition revealed that, for untreated samples at the phylum level, the bacterial community was predominantly Firmicutes (relative abundance 97.0 %), with 0.30 % Actinobacteria and 0.10 % Proteobacteria. The genus Oxobacter (35.0 %), Clostridium (12.0 %) and Ethanoligenens (10.0 %) were ubiquitous and abundant in the untreated sample. The archaeal community was however dominated by the Euryarchaeota with one methanogenic order Methanomicrobiales, and a high abundance of the genera Thermacetogenium. For pretreated samples, at the phylum level, bacterial community was also dominated by Firmicutes (95.0 %), followed by Proteobacteria (1.02 %), Actinobacteria (0.18 %) and Tenericutes (0.06 %). The genus Clostridium (41.0 %), Ethanoligenens (29.0 %) and Lactobacillus (15.0 %) were also ubiquitous and abundant in the pretreated sample. Archaeal community was also dominated by Euryarchaeota with the two methanogenic orders Methanomicrobiales and Methanosarcinales dominating. The major microbial groups were hydrolyzing and fermenting populations. These findings revealed rich microbial assemblage and diversity among microbial communities in biogas digestate.

Efficiency of an integrated process of electrooxidation and anaerobic digestion of waste activated sludge

Background Most of the organic content of waste activated sludge (WAS) comprises microbial cells hard to degrade, which must be pre-treated for the energy recovery by anaerobic digestion (AD). Electrooxidation pre-treatment (EOP) with a boron-doped diamond (BDD) electrode have been considered a promising novel technology that increase hydrolysis rate, by the disintegrating cell walls from WAS. Although electrochemical oxidation could efficiently solubilise organic substances of macromolecules, limited reports are available on EOP of WAS for improving AD. In this endeavour, the mathematical optimization study and the energy analysis of the effect of current density (CD) during EOP and the initial total solids concentration [TS] from WAS on methane (CH4) production by AD was investigated. Results In the present work, biogas production from WAS conversion are comprehensively affected by CD and [TS]. The highest COD and VS removal by 60 and 39% respectively, were achieved with WAS at 3% of [TS] pre-treated at CD of 24.1 mA/cm2, and with a maximum CH4 production of 305 N-L/kg VS and a positive energy balance of 0.83 kWh/kg VS. Therefore, the low current densities used in boron-doped diamond (BDD) electrode are adequate to produce the strong oxidant ●OH radical on the electrode surface, allow the oxidation of organic compounds that favours the solubilization of COD from WAS. Conclusions The improvement of VS removal indicates that EOP help to disintegrating cell walls from WAS. This allows a decomposition reaction that leads to biodegrade more compounds during AD. The energy balance was positive, suggesting that even without any optimization the energy used as electricity could be approximately recovered as energy from the increased methane production. However, this kind of analysis have not been sufficiently studied so far, therefore, is important to understand how critical parameters can influence the pre-treatment and AD performances. The current study highlights that the mathematical optimization and energy analysis can get the whole process more convenient and feasible.

Effects of experimental parameters on methane production and volatile solids removal from tomato and pepper plant wastes

In Mexico, protected agriculture generates large amounts of tomato and pepper plants residues (TPW and PPW, respectively). Given the limited information on methane production from anaerobic digestion of these wastes, this study aimed to determine the effects of the substrate/inoculum (S/I) ratio, temperature, and total solids content on methane production and volatile solids (VS) removal by two subsequent batch experiments (Experiments A and B). Experiment A was performed to evaluate the substrate/inoculum ratios of 0.5, 1.0, and 2.0 at room temperature (22 ± 4.5 °C). Based on the best methane yield from experiment A, a new experiment was established (Experiment B) using only tomato wastes, where temperature was kept at 29 °C and 39 °C. The total solids content was analyzed depending on the S/I ratio used. For both substrates, an S/I ratio of 0.5 was the most appropriate for methane production. The temperature had a positive effect on volatile solids removal and methane yield. In contrast, the total solids content (% TS) only had a positive effect on methane production. To the authors’ knowledge, this is the first study evaluating the effect of the S/I ratio on methane production from tomato and pepper plant wastes.

Enhanced Biogas Production from Anaerobic Codigestion of Lignocellulosic Waste for Efficient Bioenergy Utilization in Heating and Combustion Engine

Anaerobic digestion (AD) of lignocellulosic agro-waste such as coconut husk fibre, pineapple floret and banana stem was studied using standard protocols. A combination of physical, chemical and biological Pre-treatment was performed to facilitate the anaerobic digestion process. The experiment was carried out using laboratory-scale batch bioreactors maintained at 44.5 ± 2ºC and retention time of 25 days. Biogas production, pH, total and volatile solids concentrations (TS, VS) were also measured. With a general increase in pH after Pre-treatment of all substrates, biogas yield was significantly improved by 83.1% in all codigestion assays when compared to control (untreated substrates) with highest TS and VS removal rates of 77.7% and 87.2% respectively. In terms process performance, Pre-treatment of single substrate did not significantly improve AD of single substrates (coconut husk fibre/pineapple floret) and biogas production was inhibited in pre-treated banana stem. However, the highest biogas production with corresponding TS and VS removal rates of 78.3% and 92.9% respectively were obtained from untreated banana stem. Codigestion significantly enhanced biogas production that can be utilized for heating and knowledge of appropriate Pre-treatment choice is recommended to improve bioenergy production efficiency during anaerobic digestion.

Progressive Microbial Community Networks with Incremental Organic Loading Rates Underlie Higher Anaerobic Digestion Performance

ABSTRACT Although biotic interactions among members of microbial communities have been conceived to be crucial for community assembly, it remains unclear how changes in environmental conditions affect microbial interaction and consequently system performance. Here, we adopted a random matrix theory-based network analysis to explore microbial interactions in triplicate anaerobic digestion (AD) systems, which is widely applied for organic pollutant treatments. The digesters were operated with incremental organic loading rates (OLRs) from 1.0 g volatile solids (VS)/liter/day to 1.3 g VS/liter/day and then to 1.5 g VS/liter/day, which increased VS removal and methane production proportionally. Higher resource availability led to networks with higher connectivity and shorter harmonic geodesic distance, suggestive of more intense microbial interactions and quicker responses to environmental changes. Strikingly, a number of topological properties of microbial network showed significant (P < 0.05) correlation with AD performance (i.e., methane production, biogas production, and VS removal). When controlling for environmental parameters (e.g., total ammonia, pH, and the VS load), node connectivity, especially that of the methanogenic archaeal network, still correlated with AD performance. Last, we identified the Methanothermus, Methanobacterium, Chlorobium, and Haloarcula taxa and an unclassified Thaumarchaeota taxon as keystone nodes of the network. IMPORTANCE AD is a biological process widely used for effective waste treatment throughout the world. Biotic interactions among microbes are critical to the assembly and functioning of the microbial community, but the response of microbial interactions to environmental changes and their influence on AD performance are still poorly understood. Using well-replicated time series data of 16S rRNA gene amplicons and functional gene arrays, we constructed random matrix theory-based association networks to characterize potential microbial interactions with incremental OLRs. We demonstrated striking linkage between network topological features of methanogenic archaea and AD functioning independent of environmental parameters. As the intricate balance of multiple microbial functional groups is responsible for methane production, our results suggest that microbial interaction may be an important, previously unrecognized mechanism in determining AD performance.

Improved Mixing System for Anaerobic Sequencing Batch Reactors

HighlightsA novel single-jet mixing system was designed for ASBR digesters.Mixing energy was reduced to the point that solids were only partially suspended in the reactor vessel.The partial mixing system increased effluent quality as measured by suspended solids content.The partial mixing system increased solids retention, allowing hydraulic retention time (HRT) to be reduced to at least 7.5 days while maintaining solids retention time (SRT) above 100 days.The partial mixing system did not reduce biogas production rate nor biogas yield.Abstract. An anaerobic sequencing batch reactor (ASBR) is a high-rate anaerobic digestion system ideally suited for the treatment of liquids with high organic strength and low solids content. Biota are retained in an ASBR by settling solids prior to decanting effluent from the top of the reactor. Solids retention time (SRT) can be managed separately from hydraulic retention time (HRT) in an ASBR. One problem encountered with ASBRs is poor solids retention due to inefficient solids settling. A novel mixing system in which solids are only partially mixed in the reactor prior to decanting was investigated in a series of three experiments. A battery of six 30 L ASBR reactors were fed a mixture of dilute swine manure (0.30% TS, 0.20% VS) and raw glycerol. In a side-by-side comparison of two reactors operated at an organic loading rate (OLR) of 0.30 g COD L-1 d-1 with 15-day HRT and two feeding cycles per day, the partially mixed reactor outperformed the fully mixed reactor as measured by effluent quality (130 vs. 350 mg VSS L-1), SRT (354 vs. 52 days), and VS removal efficiency (88% vs. 79%). In a replicated study of five reactors operated at 0.31 g COD L-1 d-1 OLR, 15-day HRT, and two feeding cycles per day before and after switching from full to partial mixing, the partially mixed reactors showed significantly (p = 0.05) better performance as measured by effluent quality (100 vs. 382 mg VSS L-1), SRT (760 vs. 72 days), and VS removal efficiency (85% vs. 71%). Biogas production did not significantly change with the change from full to partial mixing in the five replicated reactors, i.e., average biogas yield was 0.81 and 0.77 L biogas g-1 COD with partial and full mixing, respectively. Effluent quality, SRT, VS removal efficiency, and biogas yield did not significantly change when the OLR was increased from 0.31 to 0.62 g COD L-1 d-1 and HRT was reduced from 15 to 7.5 days in a replicated study of six partially mixed reactors. A mass balance of COD across the six partially mixed reactors showed that endogenous respiration of retained biomass accounted for approximately 50% of the biogas produced by an ASBR with SRT exceeding 400 days. Keywords: Anaerobic digestion, Anaerobic sequencing batch reactor, ASBR, Biogas, Glycerol, Hydraulic retention time, Mixing, Operation, Performance, Solids retention time, Swine manure.