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.     

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.     

Pullout Response of Uniaxial Geogrid in Tire Shred–Sand Mixtures

Use of tire shred–soil mixtures as backfill materials in mechanically stabilized earth walls has several advantages over other backfill materials: (1) good drainage, (2) high shear strength, and (3) low compacted unit weight. This paper presents the results of laboratory pullout tests performed on uniaxial geogrid embedded in tire shred–sand mixtures. The effects of tire shred size, tire shred–sand mixing ratio and confining pressure on the interaction between the geogrid and tire shred–sand mixtures are evaluated. Three sizes of tire shreds are considered: tire chips (with 9.5 mm nominal size), tire shreds 50-to-100 mm long and tire shreds 100-to-200 mm in length, with mixing ratios of 0, 12, 25 and 100 % of tire shreds in the mixtures (by weight). Based on compaction testing of a number of mixtures, the optimal mixing proportion of tire shreds and sand was found to lie between 25/75 and 30/70 (by weight of tire shred and sand); this is equivalent to approximately 40/60 and 50/50, respectively, by volume of tire shreds and sand. The pullout resistance of a geogrid embedded in tire shred–sand mixtures is significantly higher than that of the same geogrid embedded in tire shreds only. The size of the tire shreds has negligible effect on the pullout resistance of a geogrid embedded in mixtures prepared with either low (12/88 mix) or high (100/0 mix) tire shred content. However, when the 25/75 mixture is used, greater geogrid pullout resistance was obtained for the geogrid embedded in tire chip–sand mixtures than in tire shred–sand mixtures.     

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.     

Utilization of constructional lime as heterogeneous catalyst in biodiesel production from waste frying oil

Waste frying oil as valueless material which is disposed to environment can be used as a promising feedstock to produce biodiesel. In this study, constructional lime was used as alkaline heterogeneous catalyst for biodiesel production from virgin and waste frying oil. After determining the best activation temperature for the catalyst (600 °C), transesterification reactions were carried out at 65 °C, MeOH to oil molar ratio of 12:1, and 1 wt% of activated constructional lime under vigorous mixing for 5 h. Yield of reactions for virgin and waste frying oil (2.17 % free fatty acid) and pretreated waste frying oil (0.918 % free fatty acid) were 87, 93.9, and 94 %, respectively. Transesterification of virgin frying oil and pretreated waste frying oil were done at 65 °C, MeOH to oil molar ratio of 6:1, and 1 wt% of KOH as catalyst under vigorous mixing for 2 h, for comparison. Yield of the reaction was 98.6 and 95.1 %, respectively. Therefore, when constructional lime is used as catalyst pretreatment of waste oil is not necessary.     

Selective digestion of industrial potato wastes for efficient biomethanation: a sustainable solution for safe environmental disposal

Potato being the staple vegetable in India is widely cultivated and processed for different value additions. During processing of potato, a huge amount of waste is generated in the form of peel and meat (mash). These wastes constitute a potential feedstock for biogas generation. The present study is focused on mitigation of acidogenesis that occurs during early stages of anaerobic digestion (AD) of potato waste which eventually inhibits the process of methanogenesis. A novel strategy of selective digestion was adopted in which the leachate and solid slurry resulting from the first stage digestion were further subjected to second stage by separating the solid and liquid phases. The obtained results indicated that stepwise digestion enhanced biomethane yield with an increase in methane percent from 46.47 to 60.4 % and reduction in total COD to about 94 %. Another novel strategy adopted in this study was the use of specifically developed microbial consortia for AD of potato wastes instead of conventional inoculum for production of biogas. The obtained yield is at par with the conventional inoculums which suggests that the developed consortia could act as potential substitute. The present study paves the way for sustainable utilization of industrial potato wastes for bioenergy production by overcoming the problems associated with conventional processes.     

Thermal treatment of waste from the meat industry in high scale rotary kiln

Recently there has been an increase in consumption of meat, especially poultry. This results in an increase in the quantity of waste, including waste feathers. Waste from the meat industry are hazardous, which must be disposed of in accordance with the law. Wastes from the meat industry normally consist of valuable elements such as phosphorus, calcium, potassium, magnesium (macronutrients), and iron, copper, zinc, manganese (micronutrients), which after suitable processing can be used for the purposes of fertilization. The paper presents the results of thermal treatment of feathers with meat and bone meal and feathers with poultry litter in a high scale rotary kiln. Mixtures of wastes were incinerated in temperature range from 600 to 900 °C for about 20–25 min. The resulting ashes were characterized by a high content of phosphorus (4–17%), calcium (17–30%) and potassium (0.6–3.6%). The study revealed that the selection of process parameters allows for obtaining ash with controlled and desired composition of macro and micronutrients, moreover, it is safe in terms of sanitary.     

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.     

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.     

Advanced technologies for the treatment of wastewaters from agro-processing industries and cogeneration of by-products: a case of slaughterhouse,dairy and beverage industries

Agro-industrial wastewaters are known by high strength of organic pollutants that cause an adverse effect on the water bodies. Wastewater management becomes a major task, leads environmental regulations to be stricter worldwide. Increased disposal of untreated/partially treated industrial wastewaters are major environmental problems in Ethiopia. In Ethiopia, industries most commonly dispose their untreated wastewater straight into the nearby rivers. Somewhat, constructed wetlands are used by some industries for treatment of wastewaters. The objective of this review paper was to summarize the characteristics and recent research efforts done on anaerobic treatment of some selected agro-industrial wastewaters and innovative technologies used for cogeneration of byproducts. Many developed countries designed cost effective approaches for agro-industrial wastewater management. The full-scale anaerobic treatment system in China generates 40,000 m³ biogas daily for 20,000 households from agro-industrial wastes. Likewise, the Brewery, Addis Ababa, Ethiopia used full-scale anaerobic treatment technology and produce average methane yield of 487 Nm³/day. The estimated maximum methane production potential of Kera, Luna slaughterhouses, and Ada milk factory were 4.5599LCH₄, 0.1878LCH₄, and 0.9952LCH₄, respectively. These indicate that they can be potential sources of biogas production. Limitations of the brewery are burning of the produced energy and some quantified parameters being become above national standards while meat processing and diary industries are discharging their wastewater without treatment into the rivers. We devised the brewery to use the produced energy properly and extend its treatment to achieve the national standards using integrated sequencing batch reactor. Similarly, slaughterhouse and diary industries should install anaerobic–aerobic integrated treatment techniques.     

Characterization and adsorption of disperse dyes from wastewater onto cenospheres activated carbon composites

In the present research, coal fly ash, a waste by-product of thermal power plant, has been segregated to obtain hollow and spherical cenospheres which combined with activated carbon in different ratio for effectual remediation of wastewater. Fabricated cenospheres activated carbon (CNAC) composites were characterized by ATR-FTIR, SEM, XRD, BET and CILAS for functionality, surface modification, crystallinity, surface area, pore volume, pore size and particle size analysis, respectively. Batch adsorption has been applied to appraised maximum removal of Disperse Orange 25 (DO) and Disperse Blue 79:1 (DB) dyes at varying solution pH 2 to 12, adsorbent dose 0.1 g cenospheres + 0.1 g AC to 1.0 g cenospheres + 1.0 g AC, dye concentration 10 to 100 mg/L, agitation speed 80 to 240 rpm and contact time 5 to 300 min at three different temperatures (25, 35 and 45 °C). The maximum percentage removal was found to be 79 and 76% for DO and DB dyes, respectively, at optimized condition. Langmuir isotherm showed good interaction with adsorption data, and the obtained maximum equilibrium adsorption capacity was found to be 90.91 mg/g for DO and 83.33 mg/g for DB at 45 °C. Eventually, the negative ?G° (? 7.513 for DO and ? 7.767 for DB) has suggested the feasibility of dyes adsorption on CNAC composites.     

Recycling of environmentally problematic plant wastes generated from greenhouse tomato crops through vermicomposting

The enormous quantity of plant waste produced from greenhouse tomato crops is an environmental problem that should be solved by recycling that waste into valuable organic products through low-cost technologies, such as vermicomposting. Feasibility of vermicomposting greenhouse tomato-plant waste (P) using paper-mill sludge (S) as complementary waste was investigated by this study. Earthworm development in P, S, and two mixtures of both wastes was monitored over 24 weeks and compared with that in cow dung (D), an optimum organic-waste to be vermicomposted. The effectiveness of vermicomposting to biostabilize those wastes was assessed by analysing phospholipid fatty acid composition, chemical features, plant-nutrient content, metal concentration, enzyme activities, and germination index (GI). A commercial vermicompost was also analyzed and taken as a reference of vermicompost quality. Earthworms did not survive in P alone, but a mixture of P with S at a ratio of 2:1 or 1:1 resulted in earthworm development similar to that observed in D. Phospholipid fatty acid analysis revealed that earthworm activity strongly transformed initial microbiota inhabiting the wastes, giving rise to vermicompost microbial communities which were similar to that of a commercial vermicompost. Both mixtures of P and S were properly biostabilized through vermicomposting, as indicated by decreases in their C:N ratio and enzyme activities together with increases in their degree of maturity (GI ~ 100 %) after the process. This study demonstrates that the vermicomposting of tomato-plant waste together with paper-mill sludge allows the recycling of both wastes, thereby improving the environmental sustainability of greenhouse crops.     

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.     

Bioremediation of heavily hydrocarbon-contaminated drilling wastes by composting

Oil-based drilling cuttings comprise a large and hazardous waste stream generated by oil and gas wells drilling operations. Oil-based cuttings are muddy materials with high contents of salts and hydrocarbons. Composting strategies have shown to be effective in the biodegradation of petroleum hydrocarbons, and it offers numerous advantages in comparison with other bioremediation methods. In order to assess the effectiveness of drilling cuttings bioremediation by composting with food and garden wastes, an experiment was conducted in 60-L reactors for 151 days. Four treatments were carried out: only oil-based cuttings, two proportions (in a volume basis) of organic wastes to drilling cuttings (33 and 75 %) and only organic wastes (as a traditional composting reference), with pine-tree woodchips as bulking agent. High degradation percentages of total hydrocarbons (≈82 %), n-alkanes (≈96 %) and the 16 USEPA-listed polycyclic aromatic hydrocarbons (≈93 %) were reached in the treatment with 75 % of organic wastes, and applying 33 % of organic wastes was not more effective than not applying organic wastes for the drilling cuttings hydrocarbons biodegradation. Furthermore, in the treatment with 75 % of organic wastes, alkanes half-life and polycyclic aromatic hydrocarbons half-life were about 10 times and four times lower, respectively, than those in the treatment with 33 % of organic wastes. Possibly, lower hydrocarbons and salts initial concentrations (i.e., lower toxicity), higher microbial counts, adequate nutrient proportions and water content supported a high biological activity with a consequent elevated biodegradation rate in the treatment with 75 % of organic wastes.     

Drainage Performance of Different Sizes Tire Chips used Alone and Mixed with Natural Aggregates as Leachate Drainage Layer Material

Results of compressibility and hydraulic conductivity testing performed under different levels of average vertical stress were used to determine the appropriate tire chips size (in particular aspect ratio) and tire chip—gravel random state mix combination. Proper sidewall treatment was provided to reduce side wall friction up to minimum level and constant head conditions were maintained with appropriate design flow rate. Results showed that tire chips (length 25 mm, aspect ratio 1) mixed with 40 mm gravel in the random state in mixing ratio of 3:1 (ds:dg) was observed to undergo minimum strain, maximum hydraulic conductivity and hence free drainage even under high vertical stress levels. By selecting tire chips of appropriate aspect ratio and optimum mix combination for the construction of drainage layer of MSW landfill leachate collection system lower strain response, higher hydraulic conductivity values and relatively free drainage even under anticipated higher vertical stress levels may be achieved.     

Engineering geological aspects of replacing a solid waste disposal site with a sanitary landfill

The current solid waste disposal site in the Mamak district of Ankara is being engulfed by the growing city. All varieties of solid wastes, including medical wastes, are stored at the present site in an irregular manner. Topographical and geological conditions at Mamak waste site are favorable for constructing a sanitary landfill. Located at the edge of a topographical depression, the site is underlain by the natural hydraulic barriers such as clay and metagreywacke. The terrestrial clay has a permeability of 10⁻⁷ to 10⁻⁸ cm/s and low to moderate values of CEC. The proposed sanitary landfill to replace the present solid waste site has a capacity of storing solid waste over 50 years. The details of base liner, final cover, toe embankment, and drainage of leachate and gas are presented in the paper.     

Utilization of waste coral for biodiesel production via transesterification of soybean oil

In the present study, the waste coral was utilized as a source of calcium oxide for transesterification of soybean oil into biodiesel (methyl esters). Characterization results revealed that the main component of the waste coral is calcium carbonate which transformed into calcium oxide when calcined above 700 °C. The Box–Behnken design of experiment was carried out, and the results were analyzed using response surface methodology. Calcination temperature, methanol– soybean oil molar ratio and catalyst concentration were chosen as variables. The methyl ester content (wt%) was response which must be maximized. A second-order model was obtained to predict methyl ester content as a function of these variables. Each variable was placed in the three low, medium and high levels (calcination temperature of 700, 800 and 900 °C; catalyst concentration of 3, 6 and 9 wt%; methanol-to-oil ratios of 12:1, 18:1 and 24:1). The optimum conditions from the experiment were found that the calcination temperature of 900 °C, catalyst concentration of 6 wt% and methanol-to-oil ratio of 12:1. Under these conditions, methyl ester content reached to 100 wt%. The waste catalyst was capable of being reused up to 4 times without much loss in the activity.     

Phosphate removal using compounds prepared from paper sludge and fly ash

Using waste as a resource to control phosphate pollution is a rising trend. This study describes the use of paper sludge (PS) and fly ash (FA), industrial solid wastes, to prepare materials with high phosphate uptake efficiency. The process consisted of pretreatment (mechanical milling), calcination, acidification (HCl), and post-treatment (aging, drying and grinding). The maximal phosphate uptake (>92 %) was achieved using PS together with FA either at PS/FA = 0.5 g/g or at PS/FA = 2.0 g/g, both calcined at 900 °C for 2 h and stirred with HCl (HCl/FA = 3 mL/g) for 1 h. With increasing calcination temperature and decreasing acid, the crystallinity of samples declined, and phosphate uptake (PU) increased. The PU process could be well described by the pseudo-second order kinetic model, while equilibrium state could be reasonably modeled by Langmuir isotherm. Neutral and weak alkaline pH promoted the PU efficiency, and 0.3 g sample/100 mL was the cost-effective dosage under the experimental conditions. The enhanced phosphate uptake of PS and FA provides alternative materials for phosphate removal from wastewater by the use of solid wastes in paper-making industries.     

Leachability of radium-226 from industrial phosphogypsum waste using some simulated natural environmental solutions

This study investigated the leaching of radium-226 from phosphogypsum (PG) waste produced from the fertilizer industry by synthetic solutions that replicate water that may contact the waste in natural conditions. The results indicated that the activity concentration of Ra-226 in the PG was 461 ± 12 Bq kg^?1 and compared with other studies carried out worldwide. The leached percentage of Ra-226 represents the exchangeable fraction loosely bounded in the matrix of the PG waste. The leached fraction of Ra-226 was 6.5 ± 0.6 and 9.0 ± 0.5% when the waste was exposed to rainwater and saline solution, respectively. It is also found that the leaching fraction increased 10–12 ± 0.4% when the waste was exposed to the admixture of saline solution containing Sr²⁺ or Ba²⁺ cations, whereas it was lowered to 4–5 ± 0.5% in the presence of carbonate or sulfate anions. When the PG is used as an economic fertilizer, the irrigation water can leach 7.8 ± 0.6% of Ra-226 that could contribute to plant uptake, thereby to animal and/or human consumption. The primary tests of the drinking water (well and tap resources) consumed by the populations surround the PG facility showed that the activity concentration of Ra-226 was below the minimum detectable activity.     

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.