- Wastewater reaching the treatment plant comes primarily from household sources but also partially from industrial sources. The plant therefore handles a mixture of wastewater from these two sources, where industrial wastewater constitutes about 15% of all wastewater at the plant.
- According to Water & Sewage Association Rules (Plant Wastewater Discharged into Sewage Systems) 2014, industrial plants are required to comply with sewage quality as specified in the rules so that they can discharge their wastewater into the municipal collection system and from there to the treatment plant.
- The purpose of these rules is to prevent discharge of materials into the sewage system that may harm sewage carrier systems, biological processes used in treating wastes, effluent quality and the quality of sludge intended for reclamation.
- The most problematic parameters from the standpoint of treatment plant processes are oils of various types, COD and metals.
- It is highly probable that the phenomenon known as ‘sludge blanket’ is caused due to the binding of sludge particles with oils. This phenomenon severely impacts the functioning of the activated sludge process and causes changes in the rate of treatment and reduction in the quality of plant effluents.
- Heavy metals may also be present at excessive levels at the industrial plants. Certain metals may harm various stages of the biological treatment processes that are based on microbial activity. However, it should be emphasized that these metals do not reach the effluents but are instead removed in the sludge.
- Deviations in pH values of the wastewater have a negative impact primarily on the collection systems.
- From the standpoint of the use of effluents for irrigation, the most problematic parameters are salinity (chlorides) and boron, which significantly reduce the variety of crops that can be watered using plant effluents. It should be emphasized that the biological treatment plant does not remove salts and boron so that they therefore must be treated at the source.
- With the establishment of water companies at many local authorities, supervision of industrial plants and enforcement has been transferred to their responsibility. New rules have been published for the quality of industrial wastewater that may be discharged into public sewage systems and treatment plants. The local water companies are responsible for enforcement of the new regulations in their jurisdictions.