Primary settling

摘要

There are many examples of primary settling systems that are ineffective. And limitations are not restricted to small tanneries, as severe problems can be found in some of the largest and most expensive treatment plants. Many configurations are possible according to the individual situation. For example there are many variables found as pretreatment. Liquors containing sulfides might be oxidised before mixing with the other discharges, and exhaust chrome liquors and drainings may be precipitated. Nevertheless, this does not always take place in practice, so the mixing stage can be in conjunction with aeration, and there may be significant quantities of tanning agents present to precipitate proteins. In all events, screening of the effluent streams before entering the primary treatment sump or tank is of great benefit. Even if only simple bar screening is used, gross solids can be readily removed. This avoids removal at a more difficult stage, reduces the volume for removal from the settling arrangement, but most importantly, avoids the risk of blockage that might occur within sludge removal.