Organic Waste Streams Research Articles

Investigation of factors affecting on the anaerobic degradation of organic waste

Although anaerobic degradation reactions of organic waste are feasible, and have been studied since 1990. However, until now, optimizing the reaction rate to get the highest methane yield is still needed. Therefore, it is necessary to optimize the operational parameters. The goal of this study is to investigate the impacts of temperature, ratio of solid waste and innoculum, and total solid percentage to the anaerobic degradation reactions. Solid waste was the mixture of water hyacinth (representative of plant components in the organic waste stream) and cow manure (ratio of water hyacinth: cow manure = 2:1). The mixture was composted until getting a homogenous texture in order to facilitate for the anaerobic digestion process. Two temperature conditions (55 oC and 37 oC), three solid wasteinoculum (S:I) ratios (1:2, 2:1, 1:1) and five percentages of total solid (30 %, 24 %, 18 %, 14 %, 10 %) were investigated. The result indicated that in the thermophilic condition (55 oC), 24 % TS, and S:I ratio of 1:2, the reactor generated the highest methane yield after 30 days.

The full-scale anaerobic digestion microbiome is represented by specific marker populations

Anaerobic digestion is a well-established microbial-based technology for the treatment of organic waste streams and subsequent biogas recovery. A robust and versatile microbial community to ensure overall stability of the process is essential. Four full-scale anaerobic digestion plants were followed for one year to link operational characteristics with microbial community composition and structure. Similarities between digesters, community dynamics and co-occurrence between bacteria and archaea within each digester were analysed. Free ammonia concentration (>200 mg N L−1) and conductivity (>30 mS cm−1) hindered acetoclastic methanogenesis by Methanosaetaceae. Thus, methanogenesis was pushed to the hydrogenotrophic pathway carried out by Methanobacteriales and Methanomicrobiales. Firmicutes dominated the overall bacterial community in each of the digesters (>50%), however, principal coordinate analysis of Bray-Curtis indices showed that each of the four digesters hosted a unique microbial community. The uniqueness of this community was related to two phylotypes belonging to the Syntrophomonas genus (Phy32 and Phy34) and to one unclassified bacterium (Phy2), which could both be considered marker populations in the community. A clear differentiation in co-occurrence of methanogens with several bacteria was observed between the different digesters. Our results demonstrated that full-scale anaerobic digestion plants show constant dynamics and co-occurrence patterns in function of time, but are unique in terms of composition, related to the presence of marker populations.

Waste-to-energy and recycling value for developing integrated solid waste management plan in Lahore

ABSTRACTThis paper aims to determine the waste-to-energy (WTE) and recycling value of municipal solid waste (MSW) for developing an integrated solid waste management (ISWM) system for Lahore, the second largest city in Pakistan. The overall generated waste in Lahore contains 58% organic waste, 25% recyclables, and 17% others. The recyclable materials including glass, paper, and plastic are generating US$ 15.3 million per year mostly by informal sector. An estimated production of 0.45 m3 CH4/kg volatile solids with total energy value of 8747.3 TJ or 2.43 TWh can be achieved if the total organic waste stream (0.57 million ton/year) dumped at Saggian landfill site is processed using anaerobic digestion technology. The estimated refused derived fuel (RDF) value for MSW, excluding metals, glass, and other inorganic waste is about 7.71 MJ/kg with total energy potential of 6191.13 TJ or 1.72 TWh/year. The presence of high volatile organic carbon and fixed carbon in textile and paper-related waste confirmed their suitability for incineration process. A significant reduction in the final volume of waste reaching to landfill can be achieved if these WTE technologies and recycling practices are in place. This will make a premise for ISWM system in Lahore based on reduce, reuse, recycle, and recovery principles. The recovered materials and energy will not only generate revenue to fund waste management activities in Lahore, but also protect the River Ravi from waste pollution.

Englés

Anaerobic digestion is a worldwide technology to treat organic waste streams, primarily due to its capacity to produce methane as renewable energy. However, there is an increasing interest on nutrient recovery (N and P), which from both environmental and economic reasons have been identified as key feature in anaerobic digestion plants. The manuscript presents a comprehensive overview on recent advances in nutrient recovery technologies applicable for anaerobic digestion systems. The review focus on N and P recovery through the use of digestates as fertilizers, struvite precipitation and biological systems such as phycoremediation (i.e. algae cultivation) and polyphosphates accumulating organisms. Keywords: Anaerobic digestion, nutrient recovery, struvite, phycoremediation, fertilizer.

Microbial Electrochemical Monitoring of Volatile Fatty Acids during Anaerobic Digestion.

Volatile fatty acid (VFA) concentration is known as an important indicator to control and optimize anaerobic digestion (AD) process. In this study, an innovative VFA biosensor was developed based on the principle of a microbial desalination cell. The correlation between current densities and VFA concentrations was first evaluated with synthetic digestate. Two linear relationships were observed between current densities and VFA levels from 1 to 30 mM (0.04 to 8.50 mA/m(2), R(2) = 0.97) and then from 30 to 200 mM (8.50 to 10.80 mA/m(2), R(2) = 0.95). The detection range was much broader than that of other existing VFA biosensors. The biosensor had no response to protein and lipid which are frequently found along with VFAs in organic waste streams from AD, suggesting the selective detection of VFAs. The current displayed different responses to VFA levels when different ionic strengths and external resistances were applied, though linear relationships were always observed. Finally, the biosensor was further explored with real AD effluents and the results did not show significance differences with those measured by GC. The simple and efficient biosensor showed promising potential for online, inexpensive, and reliable measurement of VFA levels during AD and other anaerobic processes.

Anaerobic co-digestion of agro-food waste mixtures in a fed-batch basis

ABSTRACTThe agro-food industry (including livestock) generates millions of tonnes of waste products. A solution to this sector's waste disposal challenges was explored by a joint treatment model of organic waste products from several industries. An inventory of agro-food industry organic waste streams with high potential for biogas production was carried out in a logistically viable area (Cider Region, Asturias, Spain). Three industries were selected as those with the higher potential for this study: livestock, dairy and beverage. The kinetics of anaerobic degradation and methane production of four mixtures of selected waste streams were investigated. The specific methane production at five different substrate-to-inoculum ratios (0.50, 0.75, 1.00, 1.50 and 2.00) showed a slightly decreasing trend at the higher ratios. Some hints of a synergistic effect have been observed in mixtures with higher content in milled apple waste, while antagonistic symptoms were noted in mixtures mainly composed of dairy wastes. The estimation of fluxes of waste and methane potentials in the Cider Region suggests centralised anaerobic digestion as a sustainable solution for the valorisation of livestock and agro-food wastes generated in this area. Sector-specific waste streams (livestock and agro-food industry) could cover up to 12% of regional total energy demand.

Agar Sediment Test for Assessing the Suitability of Organic Waste Streams for Recovering Nutrients by the Aquatic Worm Lumbriculus variegatus.

An agar sediment test was developed to evaluate the suitability of organic waste streams from the food industry for recovering nutrients by the aquatic worm Lumbriculus variegatus (Lv). The effects of agar gel, sand, and food quantities in the sediment test on worm growth, reproduction, and water quality were studied. Agar gel addition ameliorated growth conditions by reducing food hydrolysis and altering sediment structure. Best results for combined reproduction and growth were obtained with 0.6% agar-gel (20 ml), 10 g. fine sand, 40 g. coarse sand, and 105 mg fish food (Tetramin). With agar gel, ingestion and growth is more the result of addition of food in its original quality. Final tests with secondary potato starch sludge and wheat bran demonstrated that this test is appropriate for the comparison of solid feedstuffs and suspended organic waste streams. This test method is expected to be suitable for organic waste studies using other sediment dwelling invertebrates.

Solid Waste Management Practices at a Private Institution of Higher Learning in Nigeria

Waste generation is an intrinsic part of human existence. Waste materials are usually characterized by their nature, components and quality. Variations in quality, quantity and composition of solid waste can be linked to various factors such as cultural, economic, social and financial status of inhabitants of the particular space being studied. These distinct factors will also determine the best waste management practice to adopt. This paper captures the current institutional solid waste management in a Nigerian Private institution of higher learning. Using key-informant interview and personal field observations, the waste generation rate, pattern and characterization was made. Results showed that between 0.3 and 0.4kg/capita/day was generated daily by the students in their respective halls of residence, with population ranging from 762 – 848 students in each of the halls. All the solid wastes generated were collected using appropriate waste collection bags and mobile bin positioned at strategic corners of the university premises. The waste materials after collection were segregated into plastics, bottles, nylon and organic materials by scavengers. After these non-bidegradables were sold in the secondary market, an estimated total sum of 639,900 naira (2908.6USD) was realized daily. At this rate a total sum of 230 million Naira (1,045,454.5 USD) is realizable yearly as wealth from waste. It was concluded that if all the organic waste streams from kitchens, cafeteria and animal houses are utilized for bioenergy and organic fertilizer, the wealth to be generated would be phenomenal.

Design of anaerobic membrane bioreactors for the valorization of dilute organic carbon waste streams

Aqueous waste organics are an abundant resource generated continuously by industry and human metabolism.

Decentralized utilization of wasted organic material in urban areas: A case study in Hong Kong

Urban areas, characterized as areas with a high population density, generate large amounts of liquid and solid waste streams. Without proper treatment, these waste streams accumulate in the environment of urban areas and may lead to serious environmental problems. Contrarily, waste streams and particularly wasted organic materials contain valuable compounds, which can be biologically and/or chemically converted into products to cover the economic needs of urban areas. In this study, a concept is presented that contributes to treatment and utilization of wasted organic material in a way to (1) avoid environmental problems, (2) exploit its potential and (3) establish a recycling. In this context, technical aspects, such as hydrolysis, waste reduction, integration in urban structures and recycling of wasted organic matter, were discussed. An example of waste utilization is given based on the organic waste stream generated by a common building in Hong Kong with 640 residents. The 640 residents would generate more than 250kg of wet organic waste per day, which can be biologically hydrolyzed using decentralized processes on site. The hydrolysis of 250kg wet organic waste would result in the production of 33kg glucose, 15kg lipids, 0.6kg free amino nitrogen and 0.2kg phosphate, which can be used as nutrients in biotechnological processes or feedstocks in chemical reactions for the production of food, feed, chemicals and materials. Recycling of organic matter is not only a sustainable waste treatment, but contributes to the economy and self-sufficiency of urban areas in resource supply.

High-rate volatile fatty acid (VFA) production by a granular sludge process at low pH.

Volatile fatty acids (VFA) are proposed platform molecules for the production of basic chemicals and polymers from organic waste streams. In this study we developed a granular sludge process to produce VFA at high rate, yield and purity while minimizing potential operational costs. A lab-scale anaerobic sequencing batch reactor (ASBR) was fed with 10 g l(-1) glucose as model substrate. Inclusion of a short (2 min) settling phase before effluent discharge enabled effective granulation and very high volumetric conversion rates of 150-300 gCOD l(-1) d(-1) were observed during glucose conversion. The product spectrum remained similar at the tested pH range with acetate and butyrate as the main products, and a total VFA yield of 60-70% on chemical oxygen demand (COD) basis. The requirement for base addition for pH regulation could be reduced from 1.1 to 0.6 mol OH(-) (mol glucose)(-1) by lowering the pH from 5.5 to 4.5. Solids concentrations in the effluent were 0.6 ± 0.3 g l(-1) but could be reduced to 0.02 ± 0.01 g l(-1) by introduction of an additional settling period of 5 min. The efficient production of VFA at low pH with a virtually solid-free effluent increases the economic feasibility of waste-based chemicals and polymer production. Biotechnol.

Life cycle assessment of food waste home composting in Greece

Home composting is a waste prevention measure related to the management of the household's food waste, garden trimmings, and other smaller organic household waste streams. Thus, home composting is an alternative way of exploitation of the “biomass” generated from the households. It is an alternative to centralized composting. Biomass utilization is explicitly stated as a principle of green chemistry. The aim of this paper is presentation of the results of a case study dealing with the life cycle environmental assessment of home composting of food waste in households in Greece. The results of the study indicate that home composting is environmentally preferable over the current organic waste management situation in Greece.

Conversion of organic wastes into fly larval biomass: bottlenecks and challenges

The large volume of organic wastes and by-products produced every year usually generates environmental problems, such as water, air and soil contamination and it can be also a focus for pathogen dispersion. Sustainable waste management strategies should be developed, that can favour the value of the organic waste instead of its disposal. A sustainable strategy would be the use of the organic waste as substrate for intensive production of insect biomass. The insects associated with manure and organic waste can play a key role for the sustainable valorisation of organic waste streams as high add value products as they could be used as feed. This review is an overview of the research related with intensive insect farming of saprophagous dipteran species (flies) on manure and other organic wastes and the by-products obtained after the process. Using dipterans as recyclers of waste means that the mass-production systems of these organisms have to be efficient and competitive with other recycling systems. This review describes the possibilities of the dipterans to become active agents in waste management systems and, at the same time, an important resource of protein for feed and the main aspects and bottlenecks that have to be improved in order to achieve competitive insect farming.

Anaerobic Leaching-Bed Reactor Treating Food Waste for Organic Acid Production: Effect of Bulking Agent

Food waste was a troublesome organic waste stream, but a highly desirable substrate for anaerobic digestion to recover energy. Among the diverse reactor configurations, the leaching-bed reactor was reported to be best choice to treating the particular organic waste for platform compounds (volatile fatty acid). In this study, we carried out a series of experiments to investigate the bulking agent and pH control on process performance, and special focus was put on the biodegradability of bulking agent. The supplement of bulking agent greatly improved the leaching rate by 3.6 folds. Although the hydrolytic and acidogenic bacteria were resistant to low pH, the pH control (neutralization) caused a significantly increased volatile fatty acid (VFA) productions from 39.1 g COD/kg VSaddedto 183.4 g VFA/kg VSadded. Comparing with the undegradable bulking agent, the case with supplementing corncob as a bulking agent showed superior VFA yields (225 g COD/kg VSadded) which could be ascribed to the good adhesive properties for microorganisms and biodegradability. The ultimate analysis of the substrate (excluding the bulking agent) also showed that most of food waste was degraded with relative short reaction time. In addition, the TG/DTA and FTIR of residual corncob results indicated some components (cellulose, hemi-cellulose) were degraded, which could contribute to the additional VFA production (14 g COD/kg VSadded). This study suggested that the corncob could be considered as a good bio-compatible bulking agent for leaching-bed reactor, which not only increased the VFA productivity, but provided additional VFA production.

Inoculum selection influences the biochemical methane potential of agro-industrial substrates.

Obtaining a reliable estimation of the methane potential of organic waste streams in anaerobic digestion, for which a biochemical methane potential (BMP) test is often used, is of high importance. Standardization of this BMP test is required to ensure inter-laboratory repeatability and accuracy of the BMP results. Therefore, guidelines were set out; yet, these do not provide sufficient information concerning origin of and the microbial community in the test inoculum. Here, the specific contribution of the methanogenic community on the BMP test results was evaluated. The biomethane potential of four different substrates (molasses, bio-refinery waste, liquid manure and high-rate activated sludge) was determined by means of four different inocula from full-scale anaerobic digestion plants. A significant effect of the selected inoculum on the BMP result was observed for two out of four substrates. This inoculum effect could be attributed to the abundance of methanogens and a potential inhibiting effect in the inoculum itself, demonstrating the importance of inoculum selection for BMP testing. We recommend the application of granular sludge as an inoculum, because of its higher methanogenic abundance and activity, and protection from bulk solutions, compared with other inocula.

Co-digestion of molasses or kitchen waste with high-rate activated sludge results in a diverse microbial community with stable methane production

Kitchen waste and molasses are organic waste streams with high organic content, and therefore are interesting substrates for renewable energy production by means of anaerobic digestion. Both substrates, however, often cause inhibition of the anaerobic digestion process, when treated separately, hence, co-digestion with other substrates is required to ensure stable methane production. In this research, A-sludge (sludge harvested from a high rate activated sludge system) was used to stabilize co-digestion with kitchen waste or molasses. Lab-scale digesters were fed with A-sludge and kitchen waste or molasses for a total period of 105 days. Increased methane production values revealed a stabilizing effect of concentrated A-sludge on kitchen waste digestion. Co-digestion of molasses with A-sludge also resulted in a higher methane production. Volumetric methane production rates up to 1.53 L L−1 d−1 for kitchen waste and 1.01 L L−1 d−1 for molasses were obtained by co-digestion with A-sludge. The stabilizing effect of A-sludge was attributed to its capacity to supplement various nutrients. Microbial community results demonstrated that both reactor conditions and substrate composition determined the nature of the bacterial community, although there was no direct influence of micro-organisms in the substrate itself, while the methanogenic community profile remained constant as long as optimal conditions were maintained.

Resource recovery from anaerobic digestate: struvite crystallisation versus ammonia stripping

The wide application of anaerobic digestion for the treatment of organic waste streams and high-loaded wastewater results in the production of high quantities of anaerobic effluents. Such effluents are characterised by high nutrient content, this is why struvite crystallisation and ammonia stripping have gained interest as routes to nitrogen and phosphorus recovery. Pros and cons of both technologies have been analysed in this paper. Ammonia stripping coupled with absorption proved to be a suitable technical solution for the recovery and valorisation of the nitrogen contained in waste streams. Laboratory-scale experiments result in more than 80% of ammonia recovery using this technique. However, since the crystallisation process can simultaneously remove and recover more than 90% P and N in stoichiometric ratio (according struvite formulation) from waste streams, it is considered the preferred technique. Both processes are environmentally friendly and cost-effective in large-scale facilities although economics slightly favour the struvite formation.

Electrochemical nutrient recovery enables ammonia toxicity control and biogas desulfurization in anaerobic digestion.

Organic waste streams can be valorized and reduced in volume with anaerobic digestion (AD). An often-encountered key issue however is the high ammonium (NH4(+)) content of certain waste streams. Ammonia (NH3), in equilibrium with NH4(+), is a toxic compound to the methanogenic community, which limits the organic loading rate and endangers process stability. An electrochemical system (ES) linked to a digester could, besides recovering this nutrient, decrease NH3 toxicity through electrochemical extraction. Therefore, two digesters with and without ES attached in the recirculation loop were operated to test whether the ES could control NH3 toxicity. During periods of high ammonium loading rates, the methane (CH4) production of the ES-coupled reactor was up to 4.5 times higher compared to the control, which could be explained through simultaneous NH4(+) extraction and electrochemical pH control. A nitrogen flux of 47 g N m(–2) membrane d(–1) could be obtained in the ES-coupled reactor, resulting in a current and removal efficiency of 38 ± 5% and 28 ± 2%, respectively, at an electrochemical power input of 17 ± 2 kWh kg(–1) N. The anode also oxidized sulfide, resulting in a significantly lower H2S emission via the biogas. Lastly, limited methanogenic community dynamics pointed to a nonselective influence of the different operational conditions.

Biochemical methane potential of livestock and agri-food waste streams in the Castilla y León Region (Spain)

An inventory of agri-food industry organic waste streams with potential for biogas production was carried out in a logistically viable area of Castilla y León (Spain). The potential for methane production from 23 wastes and their mixtures was evaluated theoretically and in laboratory batch assays. Obtained methane yields ranged from 290–725mLCH4gVS−1waste, and the methane content in biogas ranged from 46–72% for raw wastes. The estimation of the regional fluxes of waste and methane potentials suggests anaerobic digestion in a centralized plant as a sustainable solution for the valorization of the organic wastes generated in this area, where up to 5% of the primary energy demand can be covered by the calculated total biogas energy potential. Sector-specific waste streams (livestock and agri-food industry) could cover up to 24% of regional total energy demand. Logistical aspects are critical in Castilla y León due to the high dispersion of the population and the industrial facilities.

Worm-it: converting organic wastes into sustainable fish feed by using aquatic worms

Due to overfishing and the use of one-third of wild fish catches for feeding farmed fish and livestock, there is a strong need for alternative sources of suitable proteins and lipids in fish feeds. Small freshwater worms of the speciesLumbriculus variegatus can be such a source based on their high protein content, variable lipid content and amino acid pattern. In addition, their production can be combined with waste reduction, as they can be grown on safe organic wastes. In this article, it was investigated whether fatty acid (FA) profile of the worms changed with feed source. Profiles of worms grown on different feeds were highly similar, but also reflected profiles of feeds. Data suggest that the worms are capable of poly-unsaturated fatty acids bioaccumulation. The worms converted different organic wastes (fish faeces and food industry sludges) with an efficient feed conversion ratio of ~1.8 (dry to wet weight) resulting in a theoretical production of 0.1-0.14 kg of fish per kg of waste. Worm composition resembles that of other live feeds and the biomass contains important FAs. Safety of organic non-feed waste streams for worm production should be further evaluated.