AEROBIC BIOLOGICAL-TREATMENT
SYSTEMS
Developments in wastewater ponds
In most countries, ponds remain the main form of
aerobic biological treatment for the removal of
COD from slaughterhouse wastewater, although a
wider variety of secondary biological systems has
also been used to some extent, including trickling
filters and activated-sludge systems. There have been
few exciting developments in the use of classical
pond types (facultative; aerated) to treat slaughterhouse
wastewater in the last decade (Sachon, 1984).
Some slaughterhouses treat hide-curing wastewater
in evaporative ponds. Tanji et al. (1992) studied
Californian evaporation ponds and found thatheavy-metal concentrations in salt evaporates were
well below hazardous levels and that, for agricultural
drainage liquids, the main salts crystallised were
relatively non-toxic sulphate, chloride and carbonate
salts of sodium, magnesium and calcium. In contrast,
it was found that concentrations of toxic heavy metals
exceeded hazardous levels in the concentrated
liquor of ponds, especially when conditions of
almost complete evaporation were approached. Care
is needed in the disposal of such liquid.
Three new concepts for ponds have emerged in
the last decade, but none have been applied to
slaughterhouse wastewater. High-rate algal ponds
involve an initial pond in which incoming wastewater
enters a deep anaerobic pond section, after which it
flows into an aerobic section. An aerobic environment
is maintained by recirculation of oxygen-rich
water from a second pond containing very high algal
concentrations. Israeli experience (domestic wastewater)
with these systems has been positive (Shelef
& Azov, 1987
AEROBIC BIOLOGICAL-TREATMENTSYSTEMSDevelopments in wastewater pondsIn most countries, ponds remain the main form ofaerobic biological treatment for the removal ofCOD from slaughterhouse wastewater, although awider variety of secondary biological systems hasalso been used to some extent, including tricklingfilters and activated-sludge systems. There have beenfew exciting developments in the use of classicalpond types (facultative; aerated) to treat slaughterhousewastewater in the last decade (Sachon, 1984).Some slaughterhouses treat hide-curing wastewaterin evaporative ponds. Tanji et al. (1992) studiedCalifornian evaporation ponds and found thatheavy-metal concentrations in salt evaporates werewell below hazardous levels and that, for agriculturaldrainage liquids, the main salts crystallised wererelatively non-toxic sulphate, chloride and carbonatesalts of sodium, magnesium and calcium. In contrast,it was found that concentrations of toxic heavy metalsexceeded hazardous levels in the concentratedliquor of ponds, especially when conditions ofalmost complete evaporation were approached. Careis needed in the disposal of such liquid.Three new concepts for ponds have emerged inthe last decade, but none have been applied toslaughterhouse wastewater. High-rate algal pondsinvolve an initial pond in which incoming wastewaterenters a deep anaerobic pond section, after which itflows into an aerobic section. An aerobic environmentis maintained by recirculation of oxygen-richwater from a second pond containing very high algalconcentrations. Israeli experience (domestic wastewater)with these systems has been positive (Shelef& Azov, 1987
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