Evaluation of flocculation and dissolved air flotation as an advanced wastewater treatment.
A bench scale study was carried out in order to evaluate the applicability of dissolved air flotation (DAF) as an advanced treatment for effluents from three different domestic wastewater treatment processes, namely: (i) a tertiary activated sludge plant; (ii) an upflow sludge blanket anaerobic reactor (UASB); and (iii) a high-rate stabilization pond.
Flotation In Water Treatment
Dissolved-air flotation is a very effective solid-liquid separation process used in water treatment, as an alternative to sedimentation, to lower the solids concentrations before granular filtration. This enables filters to be operated more effectively and cost efficiently to produce a filtered water quality suitable, after disinfection, for potable supply. Dissolved-air flotation has been specifically developed for the treatment of algal laden and coloured waters. The flocs produced by the treatment of these waters have a low settling velocity, particularly when the water temperature is low and even when polyelectrolytes are added. Treating these waters, flotation requires smaller tanks and produces better treated water quality, compared to sedimentation. Dissolved-air flotation has become accepted as an alternative to sedimentation, in particular in the Scandinavian countries and the United Kingdom, with more than 50 plants in operation or under construction. The largest dissolved-air flotation plant currently being constructed is the 315 Ml/day Frankley water treatment works in the UK.
Potable water treatment by dissolved air flotation and filtration
Pittsfield is a city of 6Q000 people, located in the Berkshire Hills of western Massachusetts. Its water sources consist of three surface reservoirs supplying approximately 56 ML/day (15 mgd) to the city and surrounding communities. Chlorination is the only water treatment provided at intake stations located near the reservoirs. The chlorinated water contains moderate to high amounts of turbidity and dissolved organic matter, which frequently exceed the revised drinking water standards.1"5 In particular, high concentrations of chlorinated hydrocarbons have been observed in the Pittsfield drinking water. The report "Drinking Water and Cancer," released on December 17, 1980, by the President's Council on Environmental Quality, found that death statistics in Illinois, New York, Louisiana, North Carolina, and Wisconsin provided fresh evidence to support an association between rectal, colon, and bladder cancer and chlorinated water. The study said the chances of dying from rectal cancer rose between 13 percent and 97 percent and noted slightly lower increases for the other two types of cancer among individuals who drank chlorinated water.6 In response to the study, the US Environmental Protection Agency (USEPA) has taken steps to lessen the risks from chlorine by requiring programs to reduce the level of chlorination by-products in water. The construction of a full-scale