Treatment of wool scouring effluent

Effluent from the wool scouring industry is considered to be the most strongly polluting waste in the whole textile industry (Anderson & Wood, 1973). It typically contains 3,000 to 21,000 mg/l wool grease, 7,000 to 15,000 mg/l suint salts (salt produced by natural excretions) and 10,000 to 30,000 mg/l dirt (sand, vegetable matter and fibre). The biological oxygen demand (BOD) and chemical oxygen demand (COD) of the effluent can be as high as 40,000 mg/l and 120,000 mg/l respectively (Anderson & Wood, 1973; Cail et al., 1986; Christoe & Bateup, 1987; Genon et al., 1986). Since wool grease can be recovered as a saleable by product (lanolin) a majority of scouring plants around the world use disc centrifuges to recover this valuable product (Chris toe & Bateup, 1987). However, only the best quality of grease (approximately 25 to 45% of the total) is removed. The concentration of grease as well as other pollutants in the final discharge is still too high for their disposal to be considered environmentally acceptable. For this reason, further treatment is required

Anaerobic bioflocculation of wool scouring effluent

A two-stage anaerobic bioflocculation process is investigated to successfully flocculate the emulsified wool grease from wool scouring effluent. After 110 days of continuous operation, the laboratory process gave promising results by removing between 70 and 90% wool grease and about 60 to 86% COD at a combined hydraulic residence time (HRT) of 4 to 10 days. Methane production and volatile fatty acids consumption were negligible. Most of the grease was thought to be removed by flocculation as a result of anaerobic activity. Since the supernatant of the treated effluent still contained residual grease of over 1 500 mg/L, further purification is necessary. The supernatant was easily treatable by the classical aerobic activated sludge treatment (internal sludge recycle), which removed virtually all of the residual wool grease resulting in less than 100 mg/l in the final effluent, at an HRT of 3 days

Treatment of wool scouring effluent by anaerobic bioflocculation

Biological destabilisation of the wool grease/water emulsion in wool scouring effluent using anaerobic bacterial activity (biological flocculation) was investigated. The aim of biological flocculation is to remove the bulk of wool grease which is the major source of COD, therefore serving as a pretreatment step, prior to classical biological processes either aerobic or anaerobic. In a semi-continuous system, a two-stage anaerobic bioflocculation process was employed to treat a high grease (> 15 g l−1) wool scouring effluent (WSE). After 110 days of operation, the process showed removal of 70 to 90% grease at a combined hydraulic residence time (HRT) of 4 to 10 days. With low grease (< 10 g l−1) WSE grease removal was lower. At an HRT of 3 days a single stage bioflocculation process removed 40% grease. The supernatant from the process was easily treated by activated sludge process reducing grease concentration from about 1.5 g l−1 to less than 0.1 g l−1 in the final effluent (HRT 3 days). Methane production of the process was negligible. Most of the grease was removed by flocculation as a result of anaerobic bacterial activity. The mechanisms of the process were investigated by a series of batch experiments and found to be; (1) appropriate gentle mixing between WSE and anaerobic sludge results in the absorption of wool grease from the liquid to the sludge phase, (2) further destablisation of the wool grease emulsion is obtained when the mixed liquor is left undisturbed. The latter was due to bacterial activity and growth on organics contained in WSE

Anaerobic bioflocculation of wool scouring effluent

A two-stage anaerobic bioflocculation process (ABP) successfully flocculated a high grease (> 15 g/l) wool scouring effluent (WSE). During 110 days of continuous operation, a two-stage laboratory process removed between 70 and 90% grease and 60-86% COD at a combined hydraulic residence time (HRT) of 4-10 days. Grease removal was more difficult with low grease (< 10 g/l) WSE. At a HRT of 3 days a single-stage ABP removed 40 and 44% grease at 20 and 37°C, respectively. Methane production and volatile fatty acids consumption were negligible. Most of the grease was removed by flocculation as a result of anaerobic bacterial activity. The supernatant was successfully treated by an aerobic activated sludge process reducing grease concentration from about 1.5 to less than 0.1 g/l in the final effluent at an HRT of 3 days. A two-stage anaerobic bioflocculation process (ABP) successfully flocculated a high grease (> 15 g/l) wool scouring effluent (WSE). During 110 days of continuous operation, a two-stage laboratory process removed between 70 and 90% grease and 60-86% COD at a combined hydraulic residence time (HRT) of 4-10 days. Grease removal was more difficult with low grease (< 10 g/l) WSE. At a HRT of 3 days a single-stage ABP removed 40 and 44% grease at 20 and 37°C, respectively. Methane production and volatile fatty acids consumption were negligible. Most of the grease was removed by flocculation as a result of anaerobic bacterial activity. The supernatant was successfully treated by an aerobic activated sludge process reducing grease concentration from about 1.5 to less than 0.1 g/l in the final effluent at an HRT of 3 days