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.
Evaluating coagulation pretreatment on poultry processing wastewater for dissolved air flotation
Eleven metal coagulants and one polyelectrolyte were assessed for their suitability in assisting a dissolved air flotation (DAF) system aimed at treating poultry processing wastewater. Preliminary jar tests determined that a combination of 800 mg/L of FeCl3 (ferric chloride) and 900 mg/L of Floccin 1115 would provide the best treatment by removing at least 98% of the total suspended solids (TSS) and 97% of the volatile suspended solids (VSS), while providing a 97% increase in water clarity. Final flotation tests suggested that the flocculated particles could be carried to the surface with 40% recycle ratio of the DAF. The resulting supernatant indicated 94.7% increase in clarity (± 1.4%), 97.3% reduction in TSS (± 0.5%), 96.6% reduction in VSS (±1.1%), 91% reduction in chemical oxygen demand (COD), and nearly 100% removal of fats, oils, and greases (FOGs). Despite the high removal efficiencies, flotation was found not to be critically necessary for treatment because the high concentration of coagulants caused settling of the flocs to occur just as rapidly. Potential coagulant overdosing is suspected at the higher end of the tested coagulant concentrations due to limited alkalinity in the wastewater. However, lack of residual metal (coagulant) ions in water may be linked to reactions leading to phosphate precipitation. The exact effect of the competing phosphate reaction on treatment efficiency is not clearly evident from this present study.
FOAM SEPARATION CLARIFICATION OF NATURAL WATERS
very turbid waters supplied in small quantities (50-500 Jackson Candle Units and 10-100 gal/hr). A promising application is the treatment of potable water supplies for company-size military installations (100-200 men), particularly overseas bases. The foam separation process is initiated by the addition to the raw water of a cationic surfactant (quaternary ammonium salt) which is adsorbed at the surfaces of the particles. The specific surfactant used in this study (cetyldimethylbenzylammonium chloride) has Food and Drug Administration approval for human ingestion of up to 40 mg/day as throat lozenges. The organophilic particles are then floated to the water surface by attachment to diffused or precipitated air bubbles and are carried into a foam phase rising above the water surface. The foam is highly concentrated in both surfactant and particulates and the water is clarified. The clarified water may then be pumped through a column of powdered active carbon to remove trace organics and (although not required) to remove the residual surfactant concentration. The