Thermal hydrolysis of raw sludge prior to mesophilic digestion is a process that has been successfully used for more than a decade. In this period it has proved to be a reliable tool for the waste water plant designer. When used as a pre treatment of mesophilic digestion, it provides increased volatile solids reduction, higher gas yields, better biosolids dewaterability and reduces the required mesophilic digestion volume.When initially deployed, the technology was very much a "Black Box" and limited information was available to allow optimum integration of the technology within the overall design of a waste water plant. This paper outlines how improved knowledge of sludge rheology, a better understanding of the steam requirements of thermal hydrolysis over the treatment cycle and a better understanding of the heat balance round the thermal hydrolysis process has allowed better integration of thermal hydrolysis within the overall works design. The paper illustrates how this knowledge has been used in the design of a 121,000 tonnes/yr thermal hydrolysis plant for United Utilities at Davyhulme, Manchester in the UK.

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Process hazard analysis (PHA) teams are responsible for determining and categorizing the potential impact of a loss of containment. For streams containing hydrogen sulfide (H₂S), the health and safety consequences of a worker being exposed to H₂S are a function of airborne concentration in the breathing zone and duration of exposure. PHA teams often do not have the technical knowledge to link the known concentration of H₂S in the process stream to an adverse health outcome. This paper describes the methodology and the assumptions made in developing such guidance. H2S concentration in the stream was correlated to concentration of H2S in the breathing zone. Vapor releases used dispersion modeling, while liquid releases required additional modeling to determine the amount of H2S liberated from the released liquid. Modeling was done on different process streams under a variety of conditions. Concentration in the breathing zone was linked to the most probable health and safety outcome by surveying relevant literature published by private and government sources. This correlated the stream concentration of H2S directly to the consequence categorization used in the PHA. Results were summarized, providing simplified guidance that is valid over a wide range of process conditions and release scenarios.

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