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.
Laboratory Comparison of DAF With Conventional Treatment
Dissolved-air flotation (DAF) was compared with conventional gravity settling (CGS) in laboratory experiments using synthetic water and in field studies using alum and polyaluminum chloride. DAF produced significantly lower residual turbidities than did CGS, particularly at colder temperatures. The difference in performance between DAF and CGS is explained using the particle size, particle density, temperature, and settlingrate relations described by Stokes' law. In addition, the large bubble volume concentrations released during DAF provided adequate opportunities for collisions between particles and bubbles, thus reducing the need for long flocculation periods. DAF achieved good performance with flocculation periods of 5 min, whereas CGS required at least 20 min of flocculation. In both processes, dissolved organic species and organic halide precursors were removed to the same degree, and similar levels of residual dissolved aluminum were found.
The removal of oil from wastewater by air flotation: A review
Oil and grease are common industrial pollutants whose removal is normally effected by gravity separation followed by a chemically enhanced air separation process. In this review, the author discusses oil and grease, their sources, their analysis, and their removal. Although removal by chemical treatment, gravity separation, and ultrafiltration are discussed initially in the article, the major thrust of the review is removal of oil by air bubbles. Discussed are the theory of flotation and equipment involved (in generating the bubbles with the discussion based on the mechanism of bubble generation), i.e., dissolved, induced, or nozzle air flotation systems. In the review, many performance data are given for numerous types of industrial wastewaters in one of several air flotation systems. The final section of the review deals with air pollution aspects, handling of the recovered product, and costs.