Epa. Vanlangerak et al., EFFECTS OF HIGH-CALCIUM CONCENTRATIONS ON THE DEVELOPMENT OF METHANOGENIC SLUDGE IN UPFLOW ANAEROBIC SLUDGE BED (UASB) REACTORS, Water research, 32(4), 1998, pp. 1255-1263
The feasibility of anaerobic treatment of wastewaters with a high calc
ium content (600-1200 mgCa(2+).l(-1)) was studied. The influence of th
e amount of precipitation and the influence of differences in biomass
yield were investigated on the development of anaerobic sludge. The ex
periments were performed in lab scale Upflow Anaerobic Sludge Blanket
(UASB) reactors, inoculated with crushed granular sludge: Four reactor
s were operated during 180 days at a constant organic loading rate of
14gCOD.l(-1).d(-1), treating completely and partly acidified wastewate
r with different calcium concentrations in the influent. Treatment of
completely acidified wastewater with a calcium concentration of 1200 m
gCa(2+).l(-1) resulted in an unstable COD removal efficiency (60-90%).
Furthermore, cementation of the sludge bed occurred after 180 days of
operation, leading to operational problems. With completely acidified
wastewater and a lower calcium concentration in the influent (600 mgC
a(2+).l(-1)), less calcium precipitated and COD removal efficiency alw
ays exceeded 98%. The cultivated sludge had a high ash content, 80-90%
, and methanogenic activity remained more or less constant at 0.7 gCOD
.gVSS(-1).d(-1). However, scaling of reactor compartments occurred und
er the latter condition. The presence of a fraction of non-acidified s
ubstrate, i.e. glucose, decreased the risk of cementation, resulted in
better granulation of the methanogenic sludge and seemed to prevent s
caling of reactor compartments. Considerable amounts of phosphate were
shown to be removed from the influent, most probably by coprecipitati
on, and incorporated in the anaerobic sludge. The results indicate tha
t anaerobic treatment of high calcium wastewaters in UASB reactors is
more feasible for partly than for completely acidified substrates. (C)
1998 Elsevier Science Ltd. All rights reserved.