Hybrid treatment systems - anaerobic ponds and trickling filters in Zimbabwe

• Published in: Water science and technology 2003-01, Vol.48 (2), p.349-356
• Main Authors: BROOME, J. M, MORRIS, P. M, NANTHAMBWE, J. G
• Format: Article
• Language: English
• Subjects: Agriculture; Anaerobic treatment; Applied sciences; Bacteria, Anaerobic - physiology; Biological and medical sciences; Biological treatment of waters; Bioreactors; Biotechnology; Conservation of Natural Resources; Decomposing organic matter; Effluent treatment; Environment and pollution; Eucalyptus; Exact sciences and technology; Filters; Filtration; Fundamental and applied biological sciences. Psychology; General purification processes; Gravitation; Gravity; Humus; Hybrid systems; Impaired water use; Industrial applications and implications. Economical aspects; Inlets (waterways); Irrigation; Irrigation tanks; Outlets; Pipework; Plantations; Pollution; Ponds; Removal; Sedimentation tanks; Sewage; Sewage treatment; Sewage treatment plants; Sludge; Tanks; Trickling filters; Waste Disposal, Fluid - methods; Wastewater treatment; Wastewater treatment plants; Wastewaters; Water Pollution - prevention & control; Water Supply; Water treatment and pollution; Zimbabwe
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.2003.0140

The most economic combination of unit treatment processes for a new sewage treatment works in Zimbabwe was found to be anaerobic ponds followed by trickling filters. The regulations governing irrigation with treated effluent permitted the omission of humus tanks or further treatment. Two stage anaerobic ponds are desludged by gravity through fixed sludge outlet pipework. Sludge is disposed of by irrigation of a Eucalyptus plantation. Novel features of the inlet works and pond outlets are also described. The works has functioned for eight years without major problems, but the assumption that humus tanks or settling ponds were not required may have been mistaken. The sludge removal system has worked well. Without the sludge pipework, it is estimated that desludging of the primary ponds would have been required after two years of operation, but they have now operated successfully for eight years. The combination of anaerobic ponds and trickling filters should be considered where land availability or site conditions make facultative ponds difficult or expensive to construct.