Organic matter accumulation during maturation of gravel-bed constructed wetlands treating farm dairy wastewaters

被引:183
作者
Tanner, CC
Sukias, JPS
Upsdell, MP
机构
[1] Natl Inst Water & Atmospher Res, Hamilton, New Zealand
[2] AgRes, Ruakura Res Ctr, Hamilton, New Zealand
关键词
constructed wetlands; wastewater treatment; dairy wastes; suspended solids; organic matter; clogging; flow tracing; hydrology; sustainability;
D O I
10.1016/S0043-1354(98)00078-5
中图分类号
X [环境科学、安全科学];
学科分类号
08 ; 0830 ;
摘要
The accumulation of organic matter (OM) was investigated after two and five years in a series of four gravel-bed constructed wetlands supplied with different hydraulic loading rates (21, 26, 46 and 72 mm d(-1)) of farm dairy wastewaters. At these hydraulic loadings, mean wastewater loadings of particulate OM (determined as volatile suspended solids) to the wetlands ranged between similar to 1.7 and 5.8 g m(.)(-2)d(.)(-1) Vertical and horizontal gradients of OM accumulation, measured by "loss on ignition", were sampled by stratified coring at 18 sites in each wetland, and their impact on wastewater residence times investigated in three of the wetlands using bromide as a conservative tracer. Mean accumulations of OM in the wetlands after five years operation ranged between 6.8 and 14.9 kg m(-2), increasing with wastewater loading rate. The annual rates of accumulation during the first two years were 1.2 to 2-fold higher than those in the subsequent three years. Around 50-60% of the OM occurred within the gravel substratum, the remainder forming surface sludges, commonly exceeding 50 mm depth over much of the wetland substratum. OM accumulation in the wetlands considerably exceeded that contributed from applied wastewaters, with wetland plant derived detritus supplying substantial additional quantities of OM. The effective void space of the wetland substrata was markedly reduced in the highest loaded wetland, with mean wastewater retention time reduced to similar to 50% of its theoretical value (corrected for evapotranspiration losses). In contrast, the lowest-loaded wetland exhibited retention times close to theoretical values. There was, however, no direct relationship between OM accumulation and the effective retention times of the wetlands, suggesting other factors, such as differences in OM bulk density, spatial patterns of accumulation and plant root growth, and inorganic accumulations, were also influencing their hydrology. (C) 1998 Elsevier Science Ltd. All rights reserved.
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页码:3046 / 3054
页数:9
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