GROSS SOLIDS IN SEWER SYSTEMS - TEMPORAL AND CATCHMENT BASED RELATIONSHIPS

The behaviour of gross and visible solids was studied at two combined sewer overflow sites using the WRc Gross Solids Sampler. At one of the sites the daily variation of gross solids during dry weather was dete rmined. There was found to be close correspondence between the variati ons of gross and suspended solids in the sewage. A relationship was de veloped between the load of gross solids and that of suspended solids at the observation point in dry weather. This relationship is presente d for use with other predictive methods. A chart is presented which di fferentiates with a high degree of reliability the gross solids produc tion of two different types of catchments, one being a collector sewer catchment, the other being a trunk. The rate of gross solids producti on has been found to be a critical factor in differentiating between t he catchments. A consistent and further differentiation in the accumul ation of gross solids is presented on the basis of antecedent dry peri od, greater than 24h allowing considerably greater accumulations than shorter dry periods.