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.

The Gippsland Water Factory (GWF) is being implemented to reclaim domestic and industrial (pulp and paper) wastewater to provide a reliable and sustainable industrial water supply, replacing the high quality raw water currently provided by Gippsland Water. A grassroots facility, the GWF will process domestic wastewater by preliminary treatment, primary sedimentation, membrane bioreactor (MBR) nutrient removal activated sludge, and reverse osmosis (RO). Domestic primary and waste activated sludge and industrial wastewater is treated in anaerobic reactors (ARs) (lagoons) prior to biological treatment via MBR. Significant H 2 S is produced in the ARs and is oxidized to elemental sulfur in the aerobic MBR by controlled oxidation. In Stage 2 of the GWF the industrial wastewater will be reclaimed using nanofiltration and RO. Extensive pilot testing supported design of the ARs and industrial MBR. Development of the GWF was based on multi-criteria analysis to create an innovative and sustainable solution. Innovative features in addition to those already mentioned include biological sulfur removal from the AR biogas and odor control which includes treatment of off-gases in the biological reactor followed by two-stage biological treatment.Glen T. Daigger (corresponding author) CH2M HILL,

No abstract

A novel process for removing sulfur from wastewater containing dissolved sulfide has been developed and implemented in a membrane bioreactor (MBR) process treating anaerobically pretreated industrial (pulp and paper) wastewater at the Gippsland Water Factory. Controlled oxygen addition to the first bioreactor zone (constituting 27.7% of the total bioreactor volume) to create oxygen-limiting conditions, followed by oxygen-sufficient conditions in the remaining zones of the bioreactor, provide the necessary conditions. Dissolved sulfide is oxidized to elemental sulfur in the first zone, and the accumulated sulfur is retained in the bioreactor mixed liquor suspended solids (MLSS) in the remaining zones. Accumulated sulfur is removed from the process in the waste activated sludge (WAS). Oxidation of dissolved sulfide to elemental sulfur reduces the associated process oxygen requirement by 75% compared to oxidation to sulfate. Microscopic examinations confirm that biological accumulation of elemental sulfur occurs. Process performance was analyzed during a nearly 2-year commissioning and optimization period. Addition of air in proportion to the process influent dissolved sulfide loading proved the most effective process control approach, followed by the maintenance of dissolved oxygen concentrations of 1.0 and 1.5 mg/L in the two downstream bioreactor zones. Sufficient oxygen is added for the stoichiometric conversion of dissolved sulfide to elemental sulfur. Enhanced biological phosphorus removal also occurred under these conditions, thereby simplifying supplemental phosphorus addition. These operating conditions also appear to lead to low and stable capillary suction time values for the MBR mixed liquor.

Gippsland Water is implementing the Gippsland Water Factory (GWF) to reclaim 35,000 m 3 /day (9.2 mgd) of municipal and industrial (pulp and paper) wastewater to a quality matching the pristine quality of the existing raw water supply. Bench-and pilot-scale testing supported multicriteria analysis to select the most sustainable approach, which consists of separate treatment in parallel treatment trains of the municipal and industrial wastewater using membrane bioreactor (MBR) technology followed by reverse osmosis (RO). Primary treatment is incorporated into the municipal treatment train, while the industrial treatment train includes anaerobic pretreatment and ozone followed by biological activated carbon (BAC) before RO to reduce fouling caused by non-biodegradable organics in the industrial MBR effluent. The industrial anaerobic pre-treatment unit is also being used to stabilize primary and waste activated sludge prior to dewatering. Sustainability considerations led to selection of anaerobic treatment to minimize energy consumption and ozone/BAC instead of chemically-intensive options to remove dissolved organics prior to RO. Facility design is incorporating green engineering and best practice environmental design standards and includes an interpretive center which will showcase the wastewater treatment technologies used and serve as a key part of an overall education program on water conservation and sustainable resource management. Use of an alliance project model facilitated collaboration and further enhanced delivery of a sustainable facility. Stage 1, which will reclaim the municipal wastewater, is currently under construction and Stage 2, which will allow reclamation of the industrial wastewater, is being planned, with offsite treatment trials to commence during August 2007. The result is a water management facility in harmony with its community that manages saline and nutrient pollution and makes fresh water while minimizing greenhouse gas impacts.