Anaerobic co-digestion of sanitary wastewater and kitchen solid waste for biogas and fertilizer production under ambient temperature: waste generated from condominium house

Addis Ababa is one of the fastest growing cities where high urbanization has become a challenge. Consequently, housing shortage is a big problem of the city. The municipality has launched a huge Condominium Housing Programme in response to the problem. However, sanitary wastewater and solid waste management are the critical problems to those houses. The wastes were collected and evaluated for its biogas production and fertilizer potential to solve the foreseen waste management problems. The physicochemical characteristics of the collected wastes were determined. A laboratory scale batch anaerobic co-digestion of both wastes with different mix ratio of 100:0, 75:25, 50:50, 25:75, and 0:100 by volume [sanitary wastewater (TS = 7,068 mg/L):kitchen organic solid waste (TS = 56, 084 mg/L)]were carried out at ambient temperature for 30 days. The amount of biogas and methane produced over the digestion period for those mixing ratios were compared. The highest biogas yield obtained from a mix ratio of 25:75 was 65.6 L, and the lowest from a mix ratio of 100:0 was 9.5 L. The percentage of methane gas in the biogas was between 19.8 and 52.8 %. From the study results, it is evidenced that the mixing ratio 25:75 produced the maximum quantity of biogas and methane. With regard to the fertilizer potential of the digested sludge, composting and sun drying process were helpful for land application by inactivating the pathogen.     

Feasibility study of waste (d) potential: co-digestion of organic wastes,synergistic effect and kinetics of biogas production

The present study investigated the synergistic effect of co-digesting food and green waste from institute campus for enhanced biogas production in different ratios in batch tests (37 ± 1 °C, 90 rpm, 45 days). The results showed that blending improved the biogas production significantly, with highest biogas yield (660 ± 24 mL g^?1 volatile solids) that was achieved at 75:25 of food and green waste ratio on volatile solids basis. The yield was 1.7- and 1.9-fold higher than the mono-digestion of food and green waste (370 ± 34; 342 ± 36 mL g^?1 volatile solids), respectively. The increase in biogas production may be attributed to optimum carbon to nitrogen ratio resulting in higher yield. The addition of TiO₂ nanoparticles showed virtually no effect on biogas production. Characterization was carried out to gain an insight of feedstocks. Modified Gompertz and logistics models were applied for kinetic study of biogas production where modified Gompertz model showed goodness of fit (R ² = 0.9978) with the experimental results.     

Experimental evaluation of anaerobic digestion for coffee wastewater treatment and its biomethane recovery potential

The objective of this study was to evaluate the performance of anaerobic digestion (AD) as an eco-friendly technology for coffee wastewater (CWW) management. First, we have characterized the CWW and found that it is suitable for microbial degradation with pH adjustment. Then, we designed a simple anaerobic batch reactor (ABR) and evaluated its potential for energy yield and efficiency to remove pollutants. The experiment was carried out by operating the anaerobic digestion (AD) for 70 days. The ABR was found to be efficient for the removal of organic load (90 %), nutrients (82 %) and suspended solids (95 %) from coffee processing waste. The increased removal efficiency of pollutants was dependent on the hydraulic retention time of the system. We also estimated that the coffee waste has a potential to produce a theoretical energy yield of 4–10 million KJ/day and an organic fertilizer (digestate) of 18.8–25.2 kg VSS/day. As a result, the AD would be a more sensible consideration as an eco-friendly treatment option for the coffee waste. The use of AD for CWW treatment not only reduces emission of greenhouse gases to the environment but also circumvents the rising demand for fuel wood and charcoal that causes a severe deforestation in the coffee growing regions of the world.     

Anaerobic digestion process: technological aspects and recent developments

The technology of anaerobic digestion allows the use of biodegradable waste for energy production by breaking down organic matter through a series of biochemical reactions. Such process generates biogas (productivity of 0.45 Nm³/KgSV), which can be used as energy source in industrial activities or as fuel for automotive vehicles. Anaerobic digestion is an economically viable and environmentally friendly process since it makes possible obtaining clean energy at a low cost and without generating greenhouse gases. Searching for clean energy sources has been the target of scientists worldwide, and this technology has excelled on the basis of efficiency in organic matter conversion into biogas (yield in the range of 0.7–2.0 kWh/m³), considered energy carriers for the future. This paper gives an overview of the technology of anaerobic digestion of food waste, describing the metabolism and microorganisms involved in this process, as well as the operational factors that affect it such as temperature, pH, organic loading, moisture, C/N ratio, and co-digestion. The types of reactors that can be used, the methane production, and the most recent developments in this area are also presented and discussed.     

Anaerobic digester sludge as nutrient source for culturing of microalgae for economic biodiesel production

After decades of ‘living dangerously’, the human kind has paused to think of Mother Nature. Alternate energy sources are being developed as a part of this realization. The use of indigenous sources of nutrients would considerably bring down the cost of production. A mixed consortium of Chlorella vulgaris, Arthrospira platensis, and tap water-originated Scenedesmus dimorphus was cultured using natural seawater, anaerobic digester sludge, and its growth was compared with synthetic commercial media like Zarrouk’s media, NaNO₃ media, and NH₄Cl media. A spectrophotometric method was standardized for regular biomass estimation. The dry biomass of a 15-day pure, batch culture of Arthrospira was found to yield around 600 mg/L in anaerobic digester sludge, whereas the pure batch culture of chlorella’s growth was hindered mainly due to the presence of bacteria and grazers. Regular microscopic observation and biomass monitoring revealed a drastic reduction in grazing activity, with the use of autoclaved AD sludge, resulting in a strong and stable microalgal mixed consortia. The consortia growth in AD sludge was found to be better than with the synthetic media with no cost of nutrient. The mixed consortia yielded a biomass up to 600 mg/L and lipid of 21.18%. The lipid generated from AD sludge had around 95% unsaturates and contained around 5% omega-3 fatty acids. The use of anaerobic digester sludge in a non-sterile condition reduces the total cost of the biodiesel production process as a whole and introduces a decentralized system for waste water treatment as well.     

A novel pilot scale multistage semidry anaerobic digestion reactor to treat food waste and cow manure

An innovative two-stage AD system to treat food waste with cow manure is presented to address the problem of ammonia inhibition and improve the stability of methanogenic reactor. The liquid digestate recirculation in the first phase was adopted to enhance the hydrolysis rate and the solubilization of organic matter. A stable long-term run (80 days) was found. The reactor configuration and the digestate post-treatment with natural zeolite led to a low ammonia concentration in reactor outlet. The biogas production in the methanogenic reactor was very stable and high: The specific biogas production in the second phase was equal to 0.68–0.92 Nm³/kg_TVSadded and the average methane concentration was equal to 85%. Good performances were also found for the first-stage digestate, with 75% soluble COD removal efficiency. The high reactor performances were related to two-stage configuration, no ammonia and VFA inhibition.     

Effects of co-substrate on biogas production from cattle manure: a review

This literature review surveys the previous and current researches on the co-digestion of anaerobic processes and examines the synergies effect of co-digestion with cattle manure. Furthermore, this review also pays attention to different operational conditions like operating temperature, organic loading rate (OLR), hydraulic retention time (HRT), chemical oxygen demand (COD) and volatile solid (VS) removal efficiency and biogas or methane production. This review shows that anaerobic mono-digestion of cattle manure usually causing poor performance and stability. Anaerobic studies were generally performed under mesophilic conditions maintained between 35 and 37 °C. Organic waste loading rate generally ranges from 1 to 6 g VS–COD L^?1 day^?1 stable condition in anaerobic digester. Generally, studies show that HRT for co-digestion of fruit–vegetables waste and industrial organic waste appears to exceed 20 days. However, the anaerobic co-digestion process is generally operated at HRT of between 10 and 20 days. VS and COD removal efficiency usually reaches up to 90 % due to co-digestion with different type organic waste. Methane–biogas production is generally obtained between 0.1 and 0.65 L CH₄–biogas g^?1 VS.     

Treatment of agricultural wastes with biogas–vermitechnology

This Article deals with the utilization of agricultural waste such as cattle manure, swine manure, chicken manure and their mixtures. It is promising a simultaneous running of biogas processes and vermitechnology. A special biogas–vermitechnological shoulder was constructed. A special organic catalyst, which contained glucose and cellulose, was used in the biogas process, as a source of biogas bacteria and to alter C/N ratio of the fermented substrate, to C/N = 30/1. Swine manure shows a higher biogas yield and methane-in-biogas content than others. It is effective to mix different manures to increase biogas yield. Earthworms Eisenia Foetida were used in the vermitechnological stage. Using only cattle manure and in mixtures with leaves (4:1 wt) was processed to make vermicompost. The obtained biohumus was studied with a microscope. It was found to have a more homogenous and structured porosity surface. It was observed that the organic content increased in vermicompost. The ratio of humic and fulvic acids can be varied using rotted leaves as fillers. Atomic Absorption Spectrometry was used to determine the content of metals. It was observed that metals from manure (Sb, Rb, Sr) were accumulated in earthworms, therefore biohumus was purified from pollutants. The released heat from the biogas stage was used for the vermitechnology stage heating. Using the biogas heat, it is possible to conduct the vermiprocess, even in cold seasons.     

Development of a master plan for industrial solid waste management

Rapid industrial growth in the province of Khuzestan in the south west of Iran has resulted in disposal of about 1750 tons of solid waste per day. Most of these industrial solid wastes including hazardous wastes are disposed without considering environmental issues. This has contributed considerably to the pollution of the environment. This paper introduces a framework in which to develop a master plan for industrial solid waste management. There are usually different criteria for evaluating the existing solid waste pollution loads and how effective the management schemes are. A multiple criteria decision making technique, namely Analytical Hierarchy Process (AHP), is used for ranking the industrial units based on their share in solid waste related environmental pollution and determining the share of each unit in total solid waste pollution load. In this framework, a comprehensive set of direct, indirect, and supporting projects are proposed for solid waste pollution control. The proposed framework is applied for industrial solid waste management in the province of Khuzestan in Iran and a databank including GIS based maps of the study area is also developed. The results have shown that the industries located near the capital city of the province, Ahwaz, produce more than 32 percent of the total solid waste pollution load of the province. Application of the methodology also has shown that it can be effectively used for development of the master plan and management of industrial solid wastes.     

Anaerobic co-digestion of sewage and brewery sludge for biogas production and land application

In Thailand, sewage sludge production from the Bangkok metropolitan area can reach up to 63,000 ton/y by 2010. The Beer-Thai Company, Thailand, produces beer and generates lots of sludge as waste. Sewage sludge and brewery sludge can be used to generate energy which could be saved on the fossil fuels conventionally used as a source of energy. The possibility was explored to mix brewery sludge with sewage sludge at different mixing ratios for anaerobic digestion so that the energy can be generated as biogas and at the same time, digested sewage sludge can be used as fertilizer for agricultural applications. A batch anaerobic reactor under mesophilic condition for a digestion period of 40 days was used in the laboratory. The acrylic reactor was cylindrical with a working weight of 12 kg. The diameter was 23.7 cm and the height was 34.5 cm. Sludge mixtures at different ratios were fed into the reactors and the optimum mixing ratio was determined. Experimental results showed that the sludge mixture at ratio of 25:75 % by weight (sewage:brewery) yielded higher biogas production. A reduction in heavy metals and pathogens was observed at this ratio after the digestion indicating its safe use as fertilizer. Nitrogen content was about 4.95 % which is well above the commercial fertilizers. At optimum mixing ratio of 25:75, the amount of the generated biogas is 1.15×10⁶ m³/y. This large amount of biogas is equivalent to 1.44 million kWh/y of electricity, 561,000 L/y of diesel oil and 936,000 L/y of vehicle gasoline.     

<Emphasis Type="Italic">Trichoderma viride</Emphasis> (MTCC 800): a potential candidate for agri-horti waste utilization by solid state fermentation

Waste management is one of the major environmental concerns globally. Meaningful utilization of various types of wastes for the production of useful products not only provides added economic benefits through variety of products but is also helpful in minimizing the environmental pollution. Trichoderma viride, a well-known fungus, has been used in the past for production of enzymes like proteases, cellulases and chitinase besides various beneficial biological activities, i.e., mycoremediation, mycoparasitism and for increasing soil fertility. In the present investigation, biodegradation potential of T. viride (MTCC-800) was evaluated by solid state fermentation using wastes like pomace, floral waste, plant litter, vegetable refuse, sawdust and sugarcane bagasse. The fungus degraded all the waste materials including sawdust that contain toxic compounds. Among all agri-horti wastes used, maximum growth of T. viride was recorded in vegetable refuse (58.16%) followed by sugarcane bagasse (48.76%) and others. The results of the present investigation, indicate that T. viride can be a potential candidate for meaningful utilization of industrial and other wastes and if. Successful at large scale it can not only help in reduction of environmental pollution but can also be a better substitute for chemical fertilizers and pesticides besides economic gains.     

Energy efficiency and environmental impact of biogas utilization in landfills

This study investigates the utilization of landfill biogas as a fuel for electrical power generation. Landfills can be regarded as conversion biogas plants to electricity, not only covering internal consumptions of the facility but contributing in the power grid as well. A landfill gas plant consists of a recovery and a production system. The recovery of landfill gas is an area of vital interest since it combines both alternative energy production and reduction of environmental impact through reduction of methane and carbon dioxide, two of the main greenhouse gases emissions. This study follows two main objectives. First, to determine whether active extraction of landfill gas in the examined municipal solid waste sites would produce adequate electric power for utilisation and grid connection and second, to estimate the reduction of sequential greenhouse gases emissions. However, in order to optimize the designing of a plant fed by biogas, it is necessary to quantify biogas production over several years. The investigation results of energy efficiency and environmental impact of biogas utilization in landfills are considering satisfactory enough both in electric energy production and in contribution to greenhouse gases mitigation.     

Evaluation of an abandoned aggregate quarry used for uncontrolled waste disposal using remote sensing technologies (Atabey,Isparta-Turkey)

Today, waste is an important environmental problem that needs to be solved. The way it is collected and managed should be considered with respect to the negative impact on the environment. Although the Atabey aggregate quarry was operated with natural sand-gravel until 2 years ago, it was closed due to technological renovation in the crushing-screening unit and uneconomic production. This area was later used by the Atabey Municipality as a waste storage area. Thus, uncontrolled storage occurred at the quarry site. As a result, new, more intensive environmental problems have emerged in the area, such as visual pollution and the pollution of groundwater. This paper evaluates the impact of municipal solid waste disposal in an abandoned quarry site on groundwater, land surface temperature, land surface moisture, and vegetation cover using GIS (Geographic Information Systems) and remote sensing technologies. According to the obtained results, the solid wastes stored in the area caused groundwater pollution, increased surface temperature, and reduced soil moisture.     

Improvement of anaerobic biodegradability of organic fraction of municipal solid waste by mechanical and thermochemical pretreatments

The effect of particle size of the organic fraction of municipal solid waste on methane potentiel was investigated and tested at different substrate-to-inoculum ratios (0.1, 0.5 and 1.0). The highest methane yield was obtained with particle size fraction > 3 mm at S/I of 0.1. Thermo-alkali and thermo-acid methods were also tested as pretreatment to increase the organic matter solubilization and subsequently methane production. The results indicated that maximum variation (63.6%) of soluble chemical oxygen demand was obtained by thermo-acid method. Optimum conditions of thermo-alkali pretreatment were pH 10, time reaction of 30 min and temperature of 105 °C. Soluble chemical oxygen demand and reducing sugar variations reached, respectively, 40 and 69% under these conditions. The methane yield of untreated and thermochemical pretreated OFMSW was determined in batch condition. The highest methane yield (260.9 L/kg VS) was obtained with thermo-alkali pretreatment, which was 21% higher than that of raw substrate. This study may pave a new way for industrial application of dealing with the organic fraction of municipal solid waste.     

Eastern Altantic fracture zones as potential disposal sites for radioactive waste

Disposal of radioactive waste in the sea floor of fracture zones associated with the flanks of the Mid-Atlantic Ridge may be a satisfactory alternative to land disposal. Effective physiographic, sedimentary, chemical, and oceanographic barriers exist in these aseismic deep canyons, especially in the eastern Atlantic. In addition, the major producers of radioactive wastes are likely to be near the Atlantic Ocean. If such a disposal strategy is adopted, intensive study of the sedimentologic and oceanographic properties of oceanic fracture zones will be necessary.     

Heavy metal accumulation in soil after application of organic wastes

Municipal solid waste compost and cattle manure are used as organic fertilizers in agriculture and horticulture. These wastes, however, may also have some negative effects on the agricultural environment. This study investigates the effects of municipal solid waste compost of Kerman (MSC) and cattle manure (CM) on availability of the heavy metal in calcareous soil (extractable with EDTA) in greenhouse conditions. The MSC and CM were mixed thoroughly with soil at rates of 0%, 2%, and 4% of dry matter. After 90 days of incubation, the soil samples were analyzed. Addition of levels of each two organic wastes into soil significantly decreased the soil pH and increased the soil EC as compared with control (unamended soil).The available contents (EDTA-extractable) of Cd, Pb, Cu, Zn, and Cu in the soil samples were increased because of each two organic treatments applied. The heavy metal contents in the soil samples amended with MSC were more than CM. The heavy metal contents of organic wastes were well below the maximum allowed by USEPA. It is recommended that in Iran, the legal maximum permissible limit for heavy elements in organic wastes must be determined.     

城市垃圾的地质处置

城市固体废物（城市垃圾）是国际上现代化城市环境污染的主要污染源之一,发达国家非常注重固体废物地质处置的研究,这一领域是环境工程与水资源工作者研究的热点问题。我国城市垃圾对环境的污染非常严重,目前有三分之二的城市已形成“垃圾包围城市”的严重局面。随着经济的发展,我国城市固体废物的数量增长很快。如何处理庞大的城市垃圾将是关系到经济发展、水资源和环境保护的重大问题。本文介绍了我国城市垃圾的现状和目前国际     

Biogass emission prognosis at the landfills

The present study aims to estimate biogas potential of two Russian landfills situated in the republic of Tatarstan and in Moscow Region. Due to environmental, economic, social and energetic consideration of biogas for human being, utilization of such a by-product would be of high concern. To date, there are seven biogas utilization projects which have been developed and implemented at municipal solid waste landfills of Russia. The purpose of the research was to determine the biogas potential at the closed landfills. During the studies held in 2008; sampling, transportation, storage of biogas and landfill soil samples, laboratory investigations; physicochemical and analytical methods for measuring of proteins, carbohydrates and fats in the organic part of the soil and the analysis of empirical data by the methods of computer modeling and mathematical statistics were carried out. The obtained results of the research; concentrations of biogas components: methane, carbon dioxide, carbon oxide, nitrogen, hydrogen and oxygen, gas flows, composition of the organic part of the fields and analysis of gas distribution on the surface of the landfills; has shown scientific and practical importance. Results could be used for the assessment of biogas potential at the landfills for further biogas utilization projects implementation with electrical or thermal energy production.     

Phototrophic bacteria dominate consortia,potentially to remove CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>S from biogas under microaerophilic conditions

The use of microbial consortia to remove contaminants in industrial systems and in natural environments could be an alternative to the use of unique strains of microorganisms, since microbial consortia have greater robustness to environmental fluctuations. However, it is necessary to evaluate the relationship between the genetic structure and functionality of the consortia. In this work, the functional and structural stability over time of two bacterial consortia (C5 and C6) with the potential to remove CO₂ and H₂S from biogas was evaluated. Both consortia decreased the dissolved CO₂ by over 30% at the end of the incubation period, but C5 presented shorter removal kinetics (3.9 days) than C6 (6.4 days). Additionally, a chemical oxidation of H₂S could have occurred in the microcosms. Moreover, both consortia presented a stable genetic structure, measured by terminal restriction fragment length polymorphism profiles of the 16S rRNA gene, characterized by high homogeneity and prevalence of the genus Rhodopseudomonas throughout the incubation period, and an increasing abundance of Xanthobacter during the exponential phase of the growth curve in C5, which would account for the functionality of the consortia.