Melbourne Water investigated a broad variety of biosolids reuse options, including energy, fuel, chemical, nutrient, and metal recovery and reuse; use of biosolids as a geotechnical fill or building material extender; and for carbon sequestration. This paper focuses on those technologies capable of recovering energy, fuels, or non-nutrient chemicals from biosolids. Recognizing the higher energy content of other feedstocks and the potential benefits from taking advantage of capital installations' economies of scale, Melbourne Water also considered receiving foreign biomass at a potential future energy recovery plant, and hauling their biosolids to off-site facilities. Technologies investigated ranged from the most established, with hundreds of installations, to the most embryonic, that have only been tested in university laboratories. Maturity, scale, feedstock suitability, costs of facilities and market conditions for products were identified for each technology.

The new Biosolids & Energy Recovery Facilities at the Irvine Ranch Water District (IRWD) Michelson Water Recycling Plant (MWRP) will include energy recovery from its anaerobic digestion biogas. As part of the design process, the IRWD conducted a study of to identify the most effective use of the biogas. The IRWD considered five biogas use options: use of biogas as an energy source for thermal drying process, cogeneration with microturbines or fuel cells, fuel source for engine driven pumps, and cleaning to near natural gas quality for injection into the natural gas pipelines. Prior to the evaluation of biogas utilization options, IRWD had identified fuel cell power generation as the preferred strategy because it maximized power generation and has the potential for financial incentives. However, as a result of the evaluation, microturbines were selected for implementation due to (1) the highest non-economic ratings, (2) cost effectiveness (only slightly higher cost than the base case), (3) lower sensitivity to fluctuations in financial incentives, and (4) added plant reliability. Key to the decision to implement microturbines rather than fuel cells is the uncertainty associated with California financial incentives.

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The latest enhancements in off-line quality control deal with the possible functional relationship between the variability of the process response and the regressors ( exper imental variables controlled by the experimenter and measured with negligible error). In the past, the analysis of experimental data generally focused on means or location parameters, and variability was only taken into account to apply generalized least squares. Currently, however, the dispersion parameters are estimated using a least squares analysis of the logarithm of the sum of the squared deviations from the within- replications mean. The adopted dispersion model is used thereafter to reduce the location model to homoscedasticity to obtain a global model, which will help to as certain the conditions that make the best of a process, i.e. minimum variance, closeness to target, and robustness to noise.

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