Selected Information - Proposed Research

The difficulty in assessing the maximum screenings and grit production rates requires very conservative specifications to be adopted for the design of screens, grit removal plant, and washer/dewatering (compaction) equipment to minimise the risk of overloading. And yet, many downstream wastewater and sludge treatment problems at existing wastewater treatment works are caused by inefficient and overloaded screens and grit removal equipment. More reliable and catchment/sewer specific information on screenings and grit production would enable optimal design and more reliable operation of screens, grit removal equipment and downstream washer/dewatering equipment. This project will.

• Develop a methodology for catchment characterisation to improve both the design of new inlet works and management of existing sewer networks and inlet works.
• Derive maximum hourly production rates of screenings and grit at existing inlet works.
• Evaluate design criteria for catchment characteristics on grit and screenings production.

Benefits to Clients

• Improved understanding of key catchment factors that influence screenings and grit production.<.li>

• More efficient designs for screens, grit removal and washing/dewatering of screenings and grit.
• Less risk of occurrences of grit and screenings overloading and impaired works' performance.
• More cost-effective operation of inlet works, less call-outs to clear blockages and improved opex forecasting.
• Better targeting of capex costs to deliver more cost-effective inlet works solutions.

Work Programme

1. Review current evidence on how screenings and grit production is affected by both catchment factors such as, sewer gradient, in-sewer storage, syphons, and pumping stations and impact of campaigns such as 'bag it and bin it'.
2. Examine how screenings and grit production vary during the first foul flush under storm flow conditions at twelve sites and how this impacts on the methods currently available for screenings and grit removal.
3. Develop a model to correlate catchment factors with screenings and sewer grit production along with evaluation of options where improvement to the catchment could be made to influence their production.

Project Outputs

• Guidance on screenings and grit production and key factors that affect production.
• Methodologies to evaluate maximum screenings and grit production during the first foul flush.
• Simple model for estimating screenings and grit production depending on catchment characteristics.
• Options to improve performance of existing screens and grit removal installations.

Related Work

• UPM (Urban Pollution Management) research and development and consultancy projects for the water industry for over 20 years.
• Sustainable recycling of sewer grits, Portfolio project CP442.
• The future of Industry Waste Streams, UKWIR, 2006.