Abstract
This work assesses the possibility of using flocculent sludge in UASB reactors applied to the treatment of dairy wastewater and studies the effect of hydraulic retention time (6, 8, 12 and 16 h) on the performance of the reactors. The results show that the performance of flocculent sludge is similar to what has been reported in literature for granular sludge. It was observed that by raising the HRT from 6 to 12 h the performance of the system is improved concerning the maximum applicable load, the COD removal efficiency and methane production, but by raising the HRT from 12 to 16 h the differences are not meaningful. To attain soluble COD removals, VFA removals and protein mineralisation near 80% and fat removals above 60% it is necessary to operate the UASB reactors at an HRT of at least 12 h. In addition to this the reactors must be operated at loads under 2.5 g COD/l•d in order to attain a conversion to methane of the removed COD above 70%. Keywords : UASB, hydraulic retention time, optimum load, flocculent biomass, dairy wastewater Water SA Vol. 31(4) 2005: 603-608
Highlights
The absence of granulation in UASB reactors used for the treatment of dairy wastewater has been considered as a major limitation to the application of this technology to this kind of complex substrates
For all the hydraulic retention time (HRT) tested the COD removal efficiency and the methane production present a somewhat sharp decrease corresponding to a certain load (3 to 6 g COD/l·d) which was lower for the smaller HRT
Some authors have previously reported a sharp decrease in the COD removal efficiency for loads above 2-4 g COD/l·d in the operation of sludge bed anaerobic reactors fed with dairy effluents (Bull et al, 1982; Shin and Paik, 1990; Morgan et al, 1991)
Summary
The absence of granulation in UASB reactors used for the treatment of dairy wastewater has been considered as a major limitation to the application of this technology to this kind of complex substrates.
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