Biological Wastes最新文献

In this paper, the kinetics and economics of substrate degradation and biogas production are discussed. Mass balance on substrate, with either the Contois or Adams-Eckenfelder models, is used to design the mathematical models of volatile solids reduction and biogas fermentation. The predictions of both the models are found to be in close agreement with the observed values reported. A computer model based on a system dynamics approach is used to model the economics of biogas production by anaerobic digestion from cattle slurry available from typical rural families in Bangladesh. This model incorporates the Adams-Eckenfelder model to determine the amount of gas production and the technique described by Audsley and Wheeler (J. Agric. Engng Res., 23, 189–201) to take into account the effects of price, interest, and inflation. The effects of changes of these parameters on the net profit or loss from the process are also considered.

This study was undertaken to evaluate the long-term effects of organic wastes on dry aggregate size distribution and on the C, N and available-P concentrations within the different aggregate fractions of some agricultural soils in North-Central Italy. Topsoils (0–20 cm) which had been amended for several years with either pig slurry (PS), cattle slurry (CS) or sewage sludge (SS) were separated into four macro-aggregate classes (4-2, 2-1, 1-0·5, 0·5-0·25 mm) and three micro-aggregate classes (0·25-0·125, 0·125-0·05 and < 0·05 mm) by dry sieving. Compared with the unamended soils, there was generally a slight increase in the proportion of the 4-2 mm macro-aggregate class following waste application. Irrespective of treatment, macro-aggregates (>0·25 mm) constituted > 70% of the total aggregate fractions.

Average increases of 17, 13 and 67% (organic C), 18, 13 and 57% (total N) and 430, 372 and 642% (available P) were obtained from additions of PS, CS and SS, respectively, and increases were found in all aggregate fractions following waste application. There was a close positive correlation between the concentrations of C, N and to a lesser extent P, in the aggregates and their silt-plus-clay contents. In terms of total contents, these elements were preferentially concentrated in the macro-aggregates. Only slight differences in the C/N ratios of the aggregates were observed but their C/P and N/P ratios decreased significantly (P ≤ 0·05) following waste application.

The solid substrate fermentation (SSF) of urea-treated wheat straw (UTWS) with Coprinus fimetarius inoculation under non-sterile conditions can bring about an increase in crude protein, digestability and digestible protein. The significant increase in the chitin and the biomass content of fermented straw correlated with the good growth of the C. fimetarius, which resulted in dry matter loss of 19·32% on day 10 of the SSF. The inoculated mould comprised 65% of the fungal isolates and from among the other native fungi identified, only Aspergillus flavus showed toxin production in pure culture. Hence, the SSF of the UTWS with C. fimetarius, as a two-stage process, can be practised at ambient temperature under non-sterile conditions.

The charred waste obtained on treatment of the bark of a tree (Terminalia tomentosa, Cambreatacea) with sulphuric acid for the manufacture of oxalic acid has been identified as a good adsorbent for toxic ions (Pb²⁺, Hg²⁺, F⁻ and Cr₂O₇²⁻) and dyes.

A heat exchanger-type furnace suitable for agricultural wastes like sugarcane bagasse, cotton stalk, coconut shell, etc., as fuel has been developed. A maximum of 90°C hot air temperature was obtained at 25·4 m³/min air flow rate at 18 kg/h of feed rate with sugarcane bagasse as fuel. With an increase in air flow, the hot air temperature decreased. It took 10·2 h to reduce the moisture content of paddy from 22·4% (wb) to 13·87% (wb) at 63°C and 33 m³/min air flow rate and 24 h for coconut (copra) from 50% (wb) to 7% (wb) at 65°C and 53·5 m³/min air flow rate in the mechanical dryer to which the furnace was supplying the hot air. There is provision to regulate the temperature of hot air by mixing in atmospheric air.

The anaerobic digestion of papermill sludge containing a high amount of inorganic matter was studied. Despite the presence of about 58% inorganic matter in the substrate, a high rate of hydrolysis and subsequent acid formation could be achieved in an acidogenic reactor which was inoculated with rumen microorganisms. Degradation efficiency of neutral detergent fibre amounted to 62% at high loading rate (34·2 g volatile solids per litre per day) and short solid retention time (51 h). In order to study the effect of accumulation of inorganic matter in the reactor, degradation efficiency was studied at various loading rates and solid retention times. An increase of solid retention time to 74 h resulted in a decreased degradation efficiency, probably due to an increased ash content in the reactor under these conditions. The effect of inorganic matter accumulation was also studied after coupling of the rumen derived acidogenic reactor to an upflow anaerobic sludge blanket-type methanogenic reactor. By using this two-stage digestion process an overall conversion of papermill sludge into biogas could be realized. The operation over about three months of the two-stage process was studied in terms of process stability, nutrient recycling and accumulation of inorganic matter.

The start-up of the dry anaerobic batch digestion by the BIOCEL-concept of the organic fraction of municipal solid waste (MSW) is unbalanced when a methanogenic inoculum (digested sewage sludge) is added to a total solids concentration of 35%. The unbalanced conditions are the result of the rapid degradation of easily-degradable compounds which are present in the organic fraction. Enhancement of the first start-up of the dry batch digestion was tried by applying an aerobic partial-composting step. By this aerobic treatment the easily degradable compounds are removed. After the composting step the anaerobic digestion will be limited by the conversion of the ligno-cellulose part of the organic fraction. It appeared that at least 19·5% of the volatile solids (VS) should be converted during the aerobic composting period before acid formation in the digestion was in balance with the methane formation. This amount of aerobically degraded VS means a 40% loss of potential biogas. The loss of a part of the biogas is a major drawback to the partial composting as a method for enhancing the start-up of the dry anaerobic digestion. A shorter composting period which is combined with another start-up method might be a feasible method to decrease the energy input of the dry digestion process.