Forced Aeration System Research Articles

Performance of different systems for the composting of the source-selected organic fraction of municipal solid waste

Performance of three pile composting systems at field-scale were studied and compared in the composting of source-selected organic fraction of municipal solid waste (OFMSW): turned pile (TP), static forced-aerated pile (SAP) and turned forced-aerated pile (TAP). Routine parameters such as temperature, oxygen content, moisture and porosity were monitored. Temperature was found to be higher in turned systems whereas oxygen content was higher in forced-aerated systems. Although the initial air-filled porosity (AFP) for all mixtures was high, around 70%, the material tended to compact in the static system. A high degree of heterogeneity was found in the non-turned system. Extent of biodegradation was measured by respiration techniques (from 5.3 to 1.1 mg [O2] g [organic matter {OM}]−1 h−1 in TP and from 4.7 to 0.7 mg [O2] g [OM]−1 h−1 in turned forced-aerated pile). The non-turned compost showed a low level of stability (3.6 mg [O2] g [OM]−1 h−1) and the lowest maturity grade (I) measured by the self-heating test. In forced-aerated systems a low intermittent aeration rate of 1 l kg [volatile solids {VS}]−1 min−1 (5 min on, 30 min off) proved to be excessive, causing major water losses and hampering moisture control. Comparison of the results obtained for TP and TAP demonstrated that the investment cost in a forced-aeration system is not necessary for this waste. Hence, turned systems are recommended for OFMSW pile composting.

Variação na pressão estática de ar insuflado em diferentes vazões específicas em colunas de material orgânico com diferentes estádios de degradação bioquímica

Little is known about the power requirements of the exhaust fan throughout the composting period of a forced aeration systems. This study was conducted in order to adjust the variation curves for static air pressure, when forced into piles of organic material at different biochemical degradation stages. To that end, a composting pile with both sugarcane bagasse (BC) and poultry litter (CF) was stacked, by preparing the mixture in such a way as to obtain an initial C/N ratio of 30/1. The material was revolved every three days during the first month, followed by revolutions at regular 5-day intervals for two more months. Load loss was measured at 1m column height for the BC under the same conditions used in the mixture, as well as in the BC + CF mixture under the conditions at 30, 60 and 90 days of composting. The higher the specific air flow and the biochemical degradation time of the material under composting, the higher the decrease in the static pressure of the air insufflated in it. The Shedd model was well adjusted to the experimental data in the air specific flow range under investigation, and can be used to predict the static pressure gradients in organic compost

Kennecott’s million-ton test heap — The active leach program

The history and results of Kennecott’s large-scale chalcopyrite leach program are presented. The program has now been underway for more than ten years. This paper describes the construction and active operation of the two-lift heap and the ancillary solvent extraction-electrowinning (SX-EW) pilot plant. The latter was used to recover the copper and provide a typical industrial raffinate for recycling to the heap. The first ore lift contained 960 kt (≈1.0 million st) of selected low-grade ore averaging 0.28% Cu, mostly in the form of chalcopyrite. The heap was leached for 18 months and gave a recovery of 27% for the block of material actually being irrigated. The second lift contained 475 kt (524,000 st) of low-grade ore averaging 0.26% Cu, also predominantly chalcopyrite. This lift was leached for 13 months with a corresponding recovery of 24.6%, including a contribution from the underlying lift. During the tests, various heap parameters were monitored, including the flow rate and composition of the pregnant leach solution, the in situ heap temperatures and oxygen contents, and the temperatures, oxygen contents and flow rates of the exhaust gases venting through the cased monitor holes on the heap. Drain-down parameters were also monitored after each leach test. Leaching continued during the drain-down periods, and the copper recovered in the drainage added another three percentage points to the total recovery. The heap profile was based on Kennecott’s earlier dump-leach modeling efforts and was intended to promote good convective airflow through the heap. This objective was met. Natural air convection provided sufficient oxygen to the heap, making the forced aeration system redundant. The SX facility consisted of a single extraction stage in series with a single strip stage (a 1×1 circuit), plus the usual tank farm equipment. The operation of the SX train was virtually trouble free with an on-line availability in excess of 98%. Partly due to the warm PLS temperatures, copper extraction efficiency averaged 95% in the first leach test and 94% in the second. Organic entrainment levels in the raffinate were typically below the limit of detection for the centrifuge method (i.e., ≤50 ppm). The EW operation included four commercial cells and had a rectifier capacity to plate 1.4 t/d (1.54 stpd) of copper. After some initial quality and operating problems were resolved, cathode quality consistently met or exceeded Comex #1 standards for impurities. By the end of the second test, the EW facility had produced 771 t (1.7 million lb) of cathode that was directly salable as a credit against the project costs.

Mathematical modelling of the composting process: A review

In this paper mathematical models of the composting process are examined and their performance evaluated. Mathematical models of the composting process have been derived from both energy and mass balance considerations, with solutions typically derived in time, and in some cases, spatially. Both lumped and distributed parameter models have been reported, with lumped parameter models presently predominating in the literature. Biological energy production functions within the models included first-order, Monod-type or empirical expressions, and these have predicted volatile solids degradation, oxygen consumption or carbon dioxide production, with heat generation derived using heat quotient factors. Rate coefficient correction functions for temperature, moisture, oxygen and/or free air space have been incorporated in a number of the first-order and Monod-type expressions. The most successful models in predicting temperature profiles were those which incorporated either empirical kinetic expressions for volatile solids degradation or CO 2 production, or which utilised a first-order model for volatile solids degradation, with empirical corrections for temperature and moisture variations. Models incorporating Monod-type kinetic expressions were less successful. No models were able to predict maximum, average and peak temperatures to within criteria of 5, 2 and 2 °C, respectively, or to predict the times to reach peak temperatures to within 8 h. Limitations included the modelling of forced aeration systems only and the generation of temperature validation data for relatively short time periods in relation to those used in full-scale composting practice. Moisture and solids profiles were well predicted by two models, but oxygen and carbon dioxide profiles were generally poorly modelled. Further research to obtain more extensive substrate degradation data, develop improved first-order biological heat production models, investigate mechanistically-based moisture correction factors, explore the role of moisture tension, investigate model performance over thermophilic composting time periods, provide more information on model sensitivity and incorporate natural ventilation aeration expressions into composting process models, is suggested.

Physical modelling of the composting environment: A review. Part 2: Simulation performance

This paper reviews previously published heat balance data for experimental and full-scale composting reactors, and then presents an evaluation of the simulation performance of laboratory and pilot-scale reactors, using both quantitative and qualitative temperature profile characteristics. The review indicates that laboratory-scale reactors have typically demonstrated markedly different heat balance behaviour in comparison to full-scale systems, with ventilative heat losses of 36–67%, and 70–95% of the total flux, respectively. Similarly, conductive/convective/radiative (CCR) heat losses from laboratory reactors have been reported at 33–62% of the total flux, whereas CCR losses from full-scale composting systems have ranged from 3% to 15% of the total. Full-scale windrow temperature-time profiles from the literature were characterised by the present authors. Areas bounded by the curve and a 40 °C baseline ( A 40) exceeded 624 °C. days, areas bounded by the curve and a 55 °C baseline ( A 55) exceeded 60 °C days, and times at 40 and 55 °C were >46 days and >24 days, respectively, over periods of 50–74 days. For forced aeration systems at full scale, values of A 40 exceeded 224 °C days, values of A 55 exceeded 26 °C days, and times at 40 and 55 °C were >14 days and >10 days, respectively, over periods of 15–35 days. Values of these four parameters for laboratory-scale reactors were typically considerably lower than for the full-scale systems, although temperature shape characteristics were often similar to those in full-scale profiles. Evaluation of laboratory-, pilot- and full-scale profiles from systems treating the same substrate showed that a laboratory-scale reactor and two pilot-scale reactors operated at comparatively high aeration rates poorly simulated full-scale temperature profiles. However, the curves from two moderately insulated, self-heating, pilot-scale reactors operated at relatively low aeration rates appeared to closely replicate full-scale temperature profiles. The importance of controlling aeration rates and CCR losses is discussed and further work suggested in order to investigate the links between simulation of the composting environment and process performance.

Isolation and Characterization of Cellulase Secreting Bacterium from Cattle Manure: Application to Composting

A extracellular cellulase producing bacterium was isolated from cow feces, and was identified to be Bacillus licheniformis on the basis of morphological and biochemical properties as well as the composition of cellular fatty acids composition (FAME). CMCase, FPase and avicelase activities of the isolates cultured in CMC media at 37°C for 24 hrs were 1.65 U/ml, 0.13 U/ml and 0.18 U/ml, respectively. However, β-glucosidase activity was not detected. The optimum pH and temperature for induction of the enzyme were 7.5 and 50°C. The maximum CMCase activity was observed at pH 7.5 and 75°C. Zymogram analysis for crude supernatant showed four major bands CMC-SDS-PAGE. By adding 0.1% DMP (Developed Microbial Product) -comp including B. licheniformis NLRI X-33, microbial product, to swine manure composting pile, the gab of composting temperature within the pile in DMP-comp and control was 23°C and 34°C, respectively, during the initial 23 day composting periods. Coliforms were not found in the swine + sawdust samples after 30 days of DMP-comp treated and 40 days of control under forced aeration system.

Performance characteristics of three aeration systems in the swine manure composting

Pilot composting of swine manure mixed with rice straw was carried out to evaluate performance characteristics of three aeration systems: forced aeration, passive aeration and natural aeration. It was expected to provide academic basis for farmers to select an advisable aeration system. The results showed that the thermophilic durations were long enough to satisfy the sanitary standard, and swine manure could reach maturity. The indexes of the composting, including physical changes, pH value, TOC, OM, TKN, WSC, WSN, solid C/N ratio, water-soluble C/N ratio, TOM, NH 4 +-N, (NO 3 −+ NO 2 −)-N, and GI had no significant difference among the treatments ( P>0.05) except the average temperature profiles ( P 12=0.001, P 13=0.036). Economic analysis showed that a passive aeration system was suitable for a small-scale swine farm, and forced aeration system should be considered to apply in the middle and large-scale swine farms with a high extent of industrialization. But, in order to avoid too high temperature occurring during composting, an active aeration control system needed to be developed.

Characterization and composting of poultry litter in forced-aeration piles

The environmental problems associated with raw poultry manure application could be mitigated by stabilizing its nutrient and organic matter (OM) contents by composting before application to agricultural soils. In the present study, quantitative changes in physical, chemical, and microbial properties of poultry litter (a mixture of poultry manure, wood shavings, waste feed, and feathers) were studied in order to understand the composting process and evaluate the suitability of the composted product as a soil amendment. The poultry litter was composted in forced-aeration piles. Results of this study showed that the poultry litter went through physico-chemical and microbial changes similar to other composting systems, including changes like self-heating of the compost mass, relative increases in total Cu, Zn, P, K, and NO x −-N and decreases in microbial population numbers, C, OM, and extractable C, Cu, Zn, and NH 4 +-N contents. Despite differences in thermophilic temperatures at different locations of the forced-aeration piles, temperatures in these locations reached ambient level almost at the same time by day 128, indicating that the poultry litter was becoming stable. Nitrogen loss was a major problem during composting of poultry litter, even when the piles were not turned under the forced-aeration system. About 18 kg of the initial N (58% of the initial N) was lost during composting, which indicates that composting reduced the value of the poultry litter as N fertilizer. However, the composted litter contained a more humified (stabilized) OM compared with the uncomposted litter, which could enhance its value as a soil conditioner. In conclusion, composting of poultry litter converted the soluble nutrients to more stable organic forms, thereby reducing their bioavailability and susceptibility to loss when applied to crop fields.

SE—Structure and Environment: Performance Characteristics of Three Aeration Systems in the Composting of Sheep Manure and Straw

Composting of sheep manure mixed with straw was carried out in a pilot plant using three different systems of aeration: pile turning; forced aeration of static pile; and passive aeration of static pile. The aim was to investigate which of these three systems was the most appropriate for the management of the manure and straw. The effects of the such composting systems on the effectiveness of composting were examined by measuring parameters such as temperature, pH, organic matter content, moisture content, changes in polysaccharide, carbon and nitrogen content. Different hydrolases activities of agricultural interest (urease, phosphatase, β -glucosidase and cellulase) which are involved in the nitrogen, phosphorous and carbon cycles were also determined. The analysis of all three composts obtained showed similar characteristics. In the passive aeration system, much of the capital and operating costs are reduced since neither the heap needs turning nor is a forced aeration system required. Besides, this system has the lowest nitrogen loss, so it could be considered as the most advisable system for small farms.

Pilot-scale reactor for aseptic solid-state cultivation

A new 50 l pilot scale reactor was used to carry out solid-state cultivations in sterile conditions using a forced aeration system with a planetary agitation device. The medium containing wheat bran wetted with a glucose solution was kept sterile for 8 days at 32°C.

Forced aeration composing of coniferous bark

A forced aeration system of composting was used to accelerate the decomposition of 14m 3 piles of Sitka spruce bark ( Picea sitchensis) for 1 month. The aeration system was similar to the Rutgers system except that greater aeration was used in the first 3 days of composting. Bioassays with tomato plants ( Solanum lycopersicum) growing on such composted bark suggested that the phytotoxicity of raw bark was reduced by this process. The optimal conditions for decomposition were composting temperatures below 60°C, urea supplementation and milled bark.