Use of solid phosphorus fractionation data to evaluate phosphorus release from waste activated sludge.

Waste activated sludge (WAS) can become an important source of phosphorus (P). P speciation was examined under anaerobic conditions, with different pH (4, 6 and 8) and temperatures (10, 20 and 35 °C). Aqueous P was measured and an extraction protocol was used to find three solid phosphorus fractions. A pH of 4 and a temperature of 35 °C gave a maximum of 51% of total P solubilized in 22 days with 50% of total P solubilized in 7 days. Batch tests indicate that little pH depression is needed to release non-apatite inorganic P (including microbial polyphosphate), while a pH of 4 rather than 6 will release more apatite inorganic P, and that organic P is relatively more difficult to release from WAS. Fractionation analysis of P in WAS can aid in design of more efficient methods for P recovery from WAS.

VFA and ammonia from residential food waste as indicators of odor potential.

Research was conducted to determine suitable chemical parameters as indicators of odor from decomposing food wastes. Prepared food scraps were stored in 18 l plastic buckets (2 kg wet weight each) at 20 °C and 8 °C to reproduce high and low temperature conditions. After 1, 3, 7, 10 and 14 days of storage, the odor from the buckets were marked to an intensity scale of 0 (no odor) to 5 (intense) and the corresponding leachate analyzed for volatile fatty acids, ammonia and total organic carbon. A linear relationship between odor intensity and the measured parameter indicates a suitable odor indicator. Odor intensified with longer storage period and warmer surroundings. The study found ammonia and isovaleric acid to be promising odor indicators. For this food waste mixture, offensive odors were emitted if the ammonia and isovaleric acid contents exceeded 360 mg/l and 940 mg/l, respectively.

Physical modelling of the composting environment: a review. Part 1: Reactor systems.

In this paper, laboratory- and pilot-scale reactors used for investigation of the composting process are described and their characteristics and application reviewed. Reactor types were categorised by the present authors as fixed-temperature, self-heating, controlled temperature difference and controlled heat flux, depending upon the means of management of heat flux through vessel walls. The review indicated that fixed-temperature reactors have significant applications in studying reaction rates and other phenomena, but may self-heat to higher temperatures during the process. Self-heating laboratory-scale reactors, although inexpensive and uncomplicated, were shown to typically suffer from disproportionately large losses through the walls, even with substantial insulation present. At pilot scale, however, even moderately insulated self-heating reactors are able to reproduce wall losses similar to those reported for full-scale systems, and a simple technique for estimation of insulation requirements for self-heating reactors is presented. In contrast, controlled temperature difference and controlled heat flux laboratory reactors can provide spatial temperature differentials similar to those in full-scale systems, and can simulate full-scale wall losses. Surface area to volume ratios, a significant factor in terms of heat loss through vessel walls, were estimated by the present authors at 5.0-88.0m(2)/m(3) for experimental composting reactors and 0.4-3.8m(2)/m(3) for full-scale systems. Non-thermodynamic factors such as compression, sidewall airflow effects, channelling and mixing may affect simulation performance and are discussed. Further work to investigate wall effects in composting reactors, to obtain more data on horizontal temperature profiles and rates of biological heat production, to incorporate compressive effects into experimental reactors and to investigate experimental systems employing natural ventilation 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 degrees C baseline (A(40)) exceeded 624 degrees C. days, areas bounded by the curve and a 55 degrees C baseline (A(55)) exceeded 60 degrees C days, and times at 40 and 55 degrees 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 degrees C days, values of A(55) exceeded 26 degrees C days, and times at 40 and 55 degrees 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.

Variations in phytoremediation performance with diesel-contaminated soil.

The potential for phytoremediation of high concentrations of petroleum hydrocarbons is poorly understood. This study examines variations in phytoremediation performance for a soil contaminated with diesel at 6400 mg TPH kg-1 dry mixture. Experiments on diesel-contaminated soil were conducted in cups using 200 g of soil, and in columns using 4,000 g. Root development and TPH levels were measured in both experiments. In addition, CO2 soil gas concentrations were measured in the column experiments. The results show that ryegrass enhanced the loss of TPH over controls, and that this benefit only became evident after full root establishment. A comparison of the two experiments shows that rooting intensity (mg root kg-1 soil) is the key factor leading to higher TPH loss rates in the smaller containers. No clear difference in TPH loss occurred at 100 and 260 mm depths. Soil gas CO2 did not correlate well with TPH loss rates. The research concludes that an understanding of root development is crucial to evaluating the potential for ryegrass phytoremediation.

Effect of compost in phytoremediation of diesel-contaminated soils.

The effect of compost on phytoremediation of diesel-contaminated soils was investigated using 130 small (200 g) containers in two screening tests. The experiments were conducted in a controlled environment using ryegrass from seed. Containers were destructively sampled at various times and analyzed for plant mass and total petroleum hydrocarbons. The results indicate that the presence of diesel reduces grass growth, and that compost helps reduced the impact of diesel on grass growth. The addition of compost helps increase diesel loss from the soils both with and without grass, though the addition of grass leads to lower diesel levels compared with controls. A second set of experiments indicates that the compost helps in phytoremediation of diesel-contaminated soil independent of the dilution effect that compost addition has. The results indicate that the compost addition allowed diesel loss down to 200 mg TPH/kg even though the compost would be expected to hold the diesel more tightly in the soil/compost mixture. The simplicity of the screening tests led to difficulties in controlling moisture content and germination rates. The conclusion of the research is that the tilling of compost into soils combined with grass seeding appears to be a valuable option for treating petroleum-contaminated soils.