A well-known cereal manufacturer has a production plant that produces coated cereals. The production process results in a high level of COD being discharged to the waste stream. For both environmental and economic reasons they needed to reduce the strength of this effluent.
Cleveland Biotech Ltd were asked to advise on possible solutions to this effluent problem. A meeting took place in February at which the details of influent waste discharge levels together with the target effluent discharge levels were provided as follows.
The effluent flow was to be taken as approximately 10,000 m3 per annum.
There was an additional and significant constraint in that any new plant would have to be restricted to an area not exceeding 10m2
Effluent Treatment PlantThe footprint available ruled out most conventional treatment plant designs such as activated sludge plants. Cleveland Biotech eventually proposed an innovative design for the plant using unorthodox pathways that allowed the effluent to be biologically degraded prior to passing through a DAF clarifier thus allowing the size of the clarifier to be considerably reduced. The proposed plant consisted of a balance tank, an aerated reaction tank and the DAF clarifier all to operate on a weekly batch basis. There was no sludge return and a system of regular bioaugmentation was built into the process in order to achieve the levels of degradation required. Cleveland Biotech formulated the microbial bioaugmentation product necessary to achieve rapid degradation of the waste and, in order to keep operational costs at an acceptable level, developed a bioreactor to grow the selected bacteria on site.
This proposal was presented and it was agreed to carry out an on site pilot plant trial in order to validate the process. A 1m3 capacity pilot plant was designed and constructed and the trial commenced at the beginning of May. The results of the trial were very encouraging achieving the levels required. A second trial was carried out in order to confirm the results. The second trial endorsed the original results. A firm proposal was made in June 1999 and the order for the plant was placed in July 1999.
Erection of the plant commenced in November and commissioning began in January. The plant was handed over in March. Since then due to production increases the level of influent COD has increased to between 30,000 and 35,000 mg/l. The process design has proved to be very robust and the plant is coping with this increase achieving 80/85% destructivity (a COD removal well above the design level of 18,000 COD) giving an environmental and economic answer to their problem.