Abstract
Anaerobic treatment of a highly alkaline fruit-cannery lye-peeling wastewater was investigated, using an upflow anaerobic sludge blanket (UASB) reactor. Only a short initialisation period was required before COD reduction and OLR had stabilised at 85 to 90% and 2.40 kgCODEm-3Ed-1, respectively. With subsequent increases in OLR to 8.1 kgCODEm-3Ed-1, the COD reduction remained between 85 and 93% and biogas production peaked at 4.1 .Ed-1 (63% methane). COD and reactor pH started to decrease after 111 d. Decreases in gas production were observed by Day 102, decreasing to 2.48 .Ed-1 by Day 111 and 0.93 .Ed-1 after 129 d. Subsequent reductions in the OLR, by reducing influent COD, had no effect on reactor stability. Loss of reactor performance was ascribed to the accumulation of sodium (potentially > 20 000 mgE.-1) within the reactor biomass, leading to inhibition of methanogenesis.
Highlights
Food-processing industries in South Africa are under increasing pressure to reduce the impact of their wastewater streams on the environment
With the promulgation of the National Environmental Management Act, Act 107 of 1998 (Republic of South Africa, 1998a) and the National Water Act, Act 36 of 1998 (Republic of South Africa, 1998b) the polluter-pays-principle has been adopted, i.e. the polluter pays for the treatment and disposal of the effluent produced
It would appear that the microbial consortium involved in the anaerobic digestion process can acclimatise to higher sodium-ion levels present in the wastewater
Summary
Food-processing industries in South Africa are under increasing pressure to reduce the impact of their wastewater streams on the environment. Disposal of cannery wastewaters is often complicated by the seasonal nature of the industry, the presence of suspended solids and particulate organics (Harada et al, 1994), cleaning solutions (most commonly sodium hydroxide), often in formulations with various chelating, softening or surfaceactive additives, nitric and phosphoric acids (Mawson, 1997) and sodium hydroxide (used during peeling of certain fruits and vegetables) in the wastewater In the past these wastewaters had been treated and disposed of by irrigation, lagooning or by means of an activated sludge process (Monson, 1959; Hanks et al, 1968; Gambrell and Peele, 1973; Stalzer, 1976) and irrigation of lye wastewaters was still practised in South Africa as recently as 2000. Most South African fruit canneries recycle their lye solutions as far as possible and dilute the rest by mixing with other cannery wastewaters
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