Developing acceptable sewage screening practices

Abstract

Severn Trent Water screens approximately 1.9 million cubic metres of sewage every day, producing 46000 m3 of screenings annually. Although the company's sludge incinerators are able to burn small quantities of screenings most of the material has to be landfilled. Over the last few years the company has investigated the areas relating to the development of an environmentally sound disposal strategy at minimum cost. These areas have included the volume and “quality” of screenings produced, the costs of collection, treatment and disposal and the variation of screenings production rates under high flow conditions. Various items of screenings handling equipment have been assessed to identify acceptable options for permanent installations. The required quality of screenings for economic disposal has been established and a “Quality Factor”, combining biological oxygen demand, density and dryness developed to provide a scientific basis to judge the aesthetic and commercial acceptability of a screenings product. This factor has been tested widely and found to coincide with visual assessment. Data on the variation of screenings production with sewage flow have been collected to assist with the sizing of future installations. The information obtained has been used to develop an application matrix for screenings handling equipment at large sewage treatment works.

Pilot-scale anaerobic digestion of screenings from wastewater treatment plants

“…The most commonly used methods of disposal for screenings in Europe are currently landfilling and incineration (Bode and Imhoff, 1996;Clay et al, 1996). Landfilling, however, is not favoured by the European waste regulations (Council directive 1999/31/EC on waste landfilling) because of (i) the required reduction of the amounts of biodegradable organic matter disposed into landfills and (ii) the ban for waste with water content above 70% w/w to be landfilled, whereas screenings often exceed this upper limit (Clay et al, 1996;Huber et al, 1995;Le Hyaric et al, 2009;Naud et al, 2007).…”

“…Landfilling, however, is not favoured by the European waste regulations (Council directive 1999/31/EC on waste landfilling) because of (i) the required reduction of the amounts of biodegradable organic matter disposed into landfills and (ii) the ban for waste with water content above 70% w/w to be landfilled, whereas screenings often exceed this upper limit (Clay et al, 1996;Huber et al, 1995;Le Hyaric et al, 2009;Naud et al, 2007). Incineration is considered as a good alternative, although the high water content is also an unfavourable characteristic that may jeopardize the operating conditions of the incineration plant in terms of combustion temperature and gaseous emissions (Bode and Imhoff, 1996).…”

The Influence of the Poles’ Lifestyle on the Quantity and Quality of Municipal Wastewater

“…The values shown are incredibly high compared to the municipal sewage COD, the value of which is usually in the range of 0.500 to 0.700 kgO2/m 3 ). These data show that the load of organic pollutants in 1m 3 of catering waste may correspond to the pollution load contained in 2,000 m 3 of municipal wastewater. The seriousness of the problem is also demonstrated by the amounts of pollutants very difficult to biological decomposition, such as fats and oils present in large quantities in catering wastewater.…”

Preliminary Treatment and Primary Sedimentation

“…Screening: The removal of floatable or suspended coarse solids in raw wastewater, which includes rags, paper, plastic, rubber, and vegetable matter (Clay et al, 1996). Bar screens are the most commonly used screening devices, with a typical spacing between bars of 15 to 25 mm (Mara, 2003).…”