Determination of biogas generation potential as a renewable energy source from supermarket wastes

Fruit, vegetable, flower waste (FVFW), dairy products waste (DPW), meat waste (MW) and sugar waste (SW) obtained from a supermarket chain were anaerobically digested, in order to recover methane as a source of renewable energy. Batch mesophilic anaerobic reactors were run at total solids (TS) ratios of 5%, 8% and 10%. The highest methane yield of 0.44 L CH₄/g VS_added was obtained from anaerobic digestion of wastes (FVFW + DPW + MW + SW) at 10% TS, with 66.4% of methane (CH₄) composition in biogas. Anaerobic digestion of mixed wastes at 5% and 8% TS provided slightly lower methane yields of 0.41 and 0.40 L CH₄/g VS_added, respectively. When the wastes were digested alone without co-substrate addition, the highest methane yield of 0.40 L CH₄/g VS_added was obtained from FVFW at 5% TS. Generally, although the volatile solids (VS) conversion percentages seemed low during the experiments, higher methane yields could be obtained from anaerobic digestion of supermarket wastes. A suitable carbon/nitrogen (C/N) ratio, proper adjustment of the buffering capacity and the addition of essential trace nutrients (such as Ni) could improve VS conversion and biogas production yields significantly.     

Kinetics assessment and modeling of biogas production by anaerobic digestion of food wastes and acclimated sewage sludge

Journal of Material Cycles and Waste Management - In this work, food wastes (FWs) and domestic sewage sludge (DSS) were used as raw materials for energy recovery by anaerobic digestion (AD). AD was...     

High-rate anaerobic digestion of sewage sludge by membrane separation solubilization coupled with UASB process

Journal of Material Cycles and Waste Management - Conventional anaerobic digestion (AD) process was often slow and thus required a large digestion tank. Upflow anaerobic sludge blanket (UASB)...     

Life cycle assessment of energy from waste via anaerobic digestion: A UK case study

Particularly in the UK, there is potential for use of large-scale anaerobic digestion (AD) plants to treat food waste, possibly along with other organic wastes, to produce biogas. This paper presents the results of a life cycle assessment to compare the environmental impacts of AD with energy and organic fertiliser production against two alternative approaches: incineration with energy production by CHP and landfill with electricity production. In particular the paper investigates the dependency of the results on some specific assumptions and key process parameters. The input Life Cycle Inventory data are specific to the Greater London area, UK. Anaerobic digestion emerges as the best treatment option in terms of total CO₂ and total SO₂ saved, when energy and organic fertiliser substitute non-renewable electricity, heat and inorganic fertiliser. For photochemical ozone and nutrient enrichment potentials, AD is the second option while incineration is shown to be the most environmentally friendly solution. The robustness of the model is investigated with a sensitivity analysis. The most critical assumption concerns the quantity and quality of the energy substituted by the biogas production. Two key issues affect the development and deployment of future anaerobic digestion plants: maximising the electricity produced by the CHP unit fuelled by biogas and to defining the future energy scenario in which the plant will be embedded.     

Single-phase and two-phase anaerobic digestion of fruit and vegetable waste: Comparison of start-up,reactor stability and process performance

Single-phase and two-phase digestion of fruit and vegetable waste were studied to compare reactor start-up, reactor stability and performance (methane yield, volatile solids reduction and energy yield). The single-phase reactor (SPR) was a conventional reactor operated at a low loading rate (maximum of 3.5 kg VS/m³ d), while the two-phase system consisted of an acidification reactor (TPAR) and a methanogenic reactor (TPMR). The TPAR was inoculated with methanogenic sludge similar to the SPR, but was operated with step-wise increase in the loading rate and with total recirculation of reactor solids to convert it into acidification sludge. Before each feeding, part of the sludge from TPAR was centrifuged, the centrifuge liquid (solubilized products) was fed to the TPMR and centrifuged solids were recycled back to the reactor. Single-phase digestion produced a methane yield of 0.45 m³ CH₄/kg VS fed and VS removal of 83%. The TPAR shifted to acidification mode at an OLR of 10.0 kg VS/m³ d and then achieved stable performance at 7.0 kg VS/m³ d and pH 5.5–6.2, with very high substrate solubilization rate and a methane yield of 0.30 m³ CH₄/kg COD fed. The two-phase process was capable of high VS reduction, but material and energy balance showed that the single-phase process was superior in terms of volumetric methane production and energy yield by 33%. The lower energy yield of the two-phase system was due to the loss of energy during hydrolysis in the TPAR and the deficit in methane production in the TPMR attributed to COD loss due to biomass synthesis and adsorption of hard COD onto the flocs. These results including the complicated operational procedure of the two-phase process and the economic factors suggested that the single-phase process could be the preferred system for FVW.     

Waste to energy: a decision-making process for technology selection through characterization of waste,considering energy and emission in the city of Ahmedabad,India

Journal of Material Cycles and Waste Management - Municipal solid waste (MSW) disposal has become major issue for the city of Ahmedabad, India. Development, concentrated population and economic...     

Adsorption removal of pollutants by active cokes produced from sludge in the energy recycle process of wastes

This study proposes a recycling system of sludge into active cokes and the fundamental examinations for the application were carried out. In the system, active cokes were produced by carbonizing pellets of sludge in a steam stream. Pyrolysis gas yielded by carbonization can be available to a fuel for a steam generation boiler. The exhaust heat from the boiler is used sequentially for drying of sludge. The active cokes are applied to the adsorbent for dioxin removal in exhaust gas from incinerators of wastes, or for purification of gas obtained in a gasification process of wastes, particularly removal of H2S. The used adsorbent is not recycled, but incinerated in the furnace without a desorption process to decompose adsorbed dioxin or to oxidize H2S for a sequential desulfurization process of SO2. Dry pellets of sludge were carbonized in a quartz tube reactor under various atmospheres. The micro pore structure and the adsorption performance of the cokes produced without activation process were examined. The micro pore structure was influenced by the temperature, the sort of flow gas (N2, CO2 and steam) and carbonization time, and the active cokes produced under the condition of the temperature 823 K for 60 min in the steam atmosphere had a largest specific surface area in the diameter less than 5 nm. The amount of benzene adsorption as an alternative substance of dioxin into the active cokes had a similar quality to a commercial active char produced from coal if it was evaluated by adsorption per a unit specific surface area. This fundamental knowledge must be reflected to an optimum design for development of a simple continuous process to produce the active cokes by a fluidized bed type of the carbonization furnace.     

Correction to: High-solids thermophilic anaerobic digestion of sewage sludge: effect of ammonia concentration

Journal of Material Cycles and Waste Management - High-solids thermophilic anaerobic digestion fed with sewage sludge of 7–8% and 9–10% total solids was investigated at the hydraulic...     

Survival of weed seeds and animal parasites as affected by anaerobic digestion at meso- and thermophilic conditions

Anaerobic digestion of residual materials from animals and crops offers an opportunity to simultaneously produce bioenergy and plant fertilizers at single farms and in farm communities where input substrate materials and resulting digested residues are shared among member farms. A surplus benefit from this practice may be the suppressing of propagules from harmful biological pests like weeds and animal pathogens (e.g. parasites). In the present work, batch experiments were performed, where survival of seeds of seven species of weeds and non-embryonated eggs of the large roundworm of pigs, Ascaris suum, was assessed under conditions similar to biogas plants managed at meso- (37 °C) and thermophilic (55 °C) conditions. Cattle manure was used as digestion substrate and experimental units were sampled destructively over time. Regarding weed seeds, the effect of thermophilic conditions (55 °C) was very clear as complete mortality, irrespective of weed species, was reached after less than 2 days. At mesophilic conditions, seeds of Avena fatua, Sinapsis arvensis, Solidago canadensis had completely lost germination ability, while Brassica napus, Fallopia convolvulus and Amzinckia micrantha still maintained low levels (～1%) of germination ability after 1 week. Chenopodium album was the only weed species which survived 1 week at substantial levels (7%) although after 11 d germination ability was totally lost. Similarly, at 55 °C, no Ascaris eggs survived more than 3 h of incubation. Incubation at 37 °C did not affect egg survival during the first 48 h and it took up to 10 days before total elimination was reached. In general, anaerobic digestion in biogas plants seems an efficient way (thermophilic more efficient than mesophilic) to treat organic farm wastes in a way that suppresses animal parasites and weeds so that the digestates can be applied without risking spread of these pests.     

Dry anaerobic digestion in batch mode: Design and operation of a laboratory-scale,completely mixed reactor

A laboratory-scale (40 l) reactor was designed to investigate dry anaerobic digestion. The reactor is equipped with an intermittent paddle mixer, enabling complete mixing in the reactor. Three consecutive batch dry digestion tests of municipal solid waste were performed under mesophilic conditions and compared to operation results obtained on a pilot-scale (21 m³) with the same feedstock. Biogas and methane production at the end of the tests were similar (around 200 m³ CH₄STP/tVS), and the dynamics of methane production and VFA accumulation concurred. However, the maximal levels of VFA transitory accumulation varied between reactors and between runs in a same reactor. Ammonia levels were similar in both reactors. These results show that the new reactor accurately imitates the conditions found in larger ones. Adaptation of micro-organisms to the waste and operating conditions was also pointed out along the consecutive batches.     

Short term effects of copper, sulfadiazine and difloxacin on the anaerobic digestion of pig manure at low organic loading rates

Antibiotics of inorganic and organic origin in pig manure can inhibit the anaerobic process in biogas plants. The influence of three frequently used antibiotics, copper dosed as CuSO₄, sulfadiazine (SDZ), and difloxacin (DIF), on the anaerobic digestion process of pig manure was studied in semi-continuous experiments. Biogas production recovered after every Cu dosage up to a sum of 12.94 g Cu kg⁻¹ organic dry matter (ODM), probably due to Cu precipitation following the formation of sulphide from sulphate. Complete inhibition was found at the very high Cu concentration of 19.40 g Cu kg⁻¹ ODM. Inhibitory effect of SDZ and DIF was observed at concentrations as high as 2.70 g kg⁻¹ ODM and 0.54 g kg⁻¹ ODM, respectively. It seems very unlikely that the antibiotics tested would inhibit the anaerobic process in a full-scale biogas plant.     

High rate mesophilic, thermophilic, and temperature phased anaerobic digestion of waste activated sludge: a pilot scale study

The paper reports the findings of a two-year pilot scale experimental trial for the mesophilic (35°C), thermophilic (55°C) and temperature phased (65+55°C) anaerobic digestion of waste activated sludge. During the mesophilic and thermophilic runs, the reactor operated at an organic loading rate of 2.2 kgVS/m(3)d and a hydraulic retention time of 20 days. In the temperature phased run, the first reactor operated at an organic loading rate of 15 kgVS/m(3)d and a hydraulic retention time of 2 days while the second reactor operated at an organic loading rate of 2.2 kgVS/m(3)d and a hydraulic retention time of 18 days (20 days for the whole temperature phased system). The performance of the reactor improved with increases in temperature. The COD removal increased from 35% in mesophilic conditions, to 45% in thermophilic conditions, and 55% in the two stage temperature phased system. As a consequence, the specific biogas production increased from 0.33 to 0.45 and to 0.49 m(3)/kgVS(fed) at 35, 55, and 65+55°C, respectively. The extreme thermophilic reactor working at 65°C showed a high hydrolytic capability and a specific yield of 0.33 g COD (soluble) per gVS(fed). The effluent of the extreme thermophilic reactor showed an average concentration of soluble COD and volatile fatty acids of 20 and 9 g/l, respectively. Acetic and propionic acids were the main compounds found in the acids mixture. Because of the improved digestion efficiency, organic nitrogen and phosphorus were solubilised in the bulk. Their concentration, however, did not increase as expected because of the formation of salts of hydroxyapatite and struvite inside the reactor.     

Correction to: Effect of feed slurry dilution and total solids on specific biogas production by anaerobic digestion in batch and semi-batch reactors

Journal of Material Cycles and Waste Management -     

Air stripping of ammonia from pig slurry: characterisation and feasibility as a pre- or post-treatment to mesophilic anaerobic digestion

The objective of the present paper has been to study the effect of pig slurry waste type, fresh or anaerobically digested, and the effect of initial pH on ammonia air stripping from pig slurry waste at high temperature (80 degrees C). Stripping process as pre- or post-treatment to anaerobic digestion has been also evaluated. Treatment performances differ according to pig slurry type. When fresh pig slurry is used, despite working at 80 degrees C, a high initial pH (11.5) is required for complete ammonia removal. On the other hand, for digested pig slurry, complete ammonia removal without pH modification is possible and organic matter significantly less contaminates recovered ammonia salt. Batch anaerobic tests showed that ammonia air stripping is not an advisable pre-treatment to pig slurry anaerobic digestion.     

A review of corn masa processing residues: generation, properties, and potential utilization

The production of corn masa-based products in the US has been increasing over the last several years, and as a result, so has the quantity of waste materials being generated from this industry. Although currently landfilled, these byproduct streams may have potential for value-added processing and utilization, which are options that simultaneously hold the promise of increased economic benefit for masa processors as well as decreased potential pollution for the environment. Fundamental to any byproduct development effort is knowledge of the characteristics of the residue stream, because physical and chemical properties are vital for the proper design of subsequent processing operations and applications. Data for masa byproduct materials are currently not readily available, however. Thus, the objective of this study was to fully investigate, review, and summarize the existing literature in order to develop a comprehensive knowledge base for these residue streams. The most substantial findings from this study were that masa residues currently are not being utilized as coproducts, but instead are being landfilled; they have a high fiber content, and thus much untapped potential exists for its extraction and value-added utilization vis-à-vis human and industrial applications, including phytosterol and ethanol production. It was also determined that masa byproducts, due to the high fiber content, may also be suitable for use as livestock feed additives, especially for ruminant animals that can digest these materials. Furthermore, due to substantial calcium content, masa byproducts could also potentially be used as a calcium resource. Under current processing practices, though, these residues have very high moisture contents. Before they can be effectively and economically utilized, they must be dehydrated in order to reduce transportation costs, decrease microbial activity, and increase shelf life.     

“二级厌氧-微氧-好氧”组合工艺处理模拟碳纤维生产废水

对模拟碳纤维生产废水进行“厌氧-好氧”静态小试,根据COD的去除效果确定该碳纤维废水的可生化性。采用“二级厌氧-微氧-好氧”组合工艺进行动态中试,考察废水的处理效果及系统的抗冲击性能。试验结果表明：该工艺对碳纤维生产废水的处理效果较好;系统具有厌氧池出水pH增大的特点,且抗冲击能力较强;在厌氧池水温为28~38 ℃、好氧池水温不低于15 ℃、废水流量为100 L/h、进水COD为660 mg/L、进水ρ（氨氮）为4.9 mg/L的条件下,出水COD稳定在50 mg/L以下,ρ（氨氮）稳定在5 mg/L以下,能够满足GB 8978-1996《污水综合排放标准》的要求。     

Comparison of different procedures to stabilize biogas formation after process failure in a thermophilic waste digestion system: influence of aggregate formation on process stability

Following a process failure in a full-scale biogas reactor, different counter measures were undertaken to stabilize the process of biogas formation, including the reduction of the organic loading rate, the addition of sodium hydroxide (NaOH), and the introduction of calcium oxide (CaO). Corresponding to the results of the process recovery in the full-scale digester, laboratory experiments showed that CaO was more capable of stabilizing the process than NaOH. While both additives were able to raise the pH to a neutral milieu (pH>7.0), the formation of aggregates was observed particularly when CaO was used as the additive. Scanning electron microscopy investigations revealed calcium phosphate compounds in the core of the aggregates. Phosphate seemed to be released by phosphorus-accumulating organisms, when volatile fatty acids accumulated. The calcium, which was charged by the CaO addition, formed insoluble salts with long chain fatty acids, and caused the precipitation of calcium phosphate compounds. These aggregates were surrounded by a white layer of carbon rich organic matter, probably consisting of volatile fatty acids. Thus, during the process recovery with CaO, the decrease in the amount of accumulated acids in the liquid phase was likely enabled by (1) the formation of insoluble calcium salts with long chain fatty acids, (2) the adsorption of volatile fatty acids by the precipitates, (3) the acid uptake by phosphorus-accumulating organisms and (4) the degradation of volatile fatty acids in the aggregates. Furthermore, this mechanism enabled a stable process performance after re-activation of biogas production. In contrast, during the counter measure with NaOH aggregate formation was only minor resulting in a rapid process failure subsequent the increase of the organic loading rate.     

Waste on the roadside, 'poi-sute' waste: its distribution and elution potential of pollutants into environment

Waste on the roadside, 'poi-sute' waste, was collected in a typical suburb in Japan (Ueda city, the sampling course: 3.2 km). The distribution, characterization of the 'poi-sute' waste and the loading of pollutants from the waste were studied. The average number of pieces of total waste was 690 pieces a month, and 220 pieces of waste were dumped a month per km. There was a tendency for much waste to be discarded around shops staying open until late at night. Regarding the sorts of the waste, cigarette butts are the most prevalent (the average was 150 cigarette butts/km/mo), and second was plastic materials. As for the weight, cigarette butts, plastics and papers were at a similar level (about 90 g/km/mo). The elution of arsenic (0.041 mg/L) and nicotine (3.8 mg/L) was ascertained by a dissolution test of 'poi-sute' cigarette butts obtained by sampling. Furthermore, the loading of heavy metals, such as lead, copper, chromium and cadmium, and polycyclic aromatic hydrocarbons (PAHs) from cigarette butts into the environment was confirmed. The load potentials of heavy metals were 0.020-1.7 mg/km/mo, and that of total-polyaromatic hydrocarbons was 0.032 mg/km/mo. These results indicate that the 'poi-sute' waste has a harmful influence on the environment.     

Waste generation in traditional organized bazaars: a case study of organic waste sources in Da Nang City,Viet Nam

Journal of Material Cycles and Waste Management - Traditional organized bazaars are important retail venues in Viet Nam, but there are concerns about their waste management programs. This study...