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To choose an appropriate dilution ratio to treat woodwaste leachate without inhibition on heterotrophic bacteria, microbial ATP concentration and the rates of heterotrophic leucine incorporation and acetate uptake were compared across surface flow mesocosm wetlands fed with different strengths of influent. Abundances of protozoa and respiring bacteria were investigated in two mesocosm wetlands to elucidate the effects of influent strength on heterotrophic bacteria. The strongest influent or the raw leachate did not show a significant inhibitory effect on leucine incorporation and acetate uptake. Instead, leucine incorporation rates by bacteria in water, epiphytic biofilm and sediment were higher in mesocosm wetlands fed with a stronger influent. There were significantly more respiring planktonic bacteria (451 x 10(5) mL(-1)) and fewer nanoflagellates (3.8 x 10(3) mL(-1)) in the mesocosm fed with a strong influent, while fewer respiring planktonic bacteria (38.7 x 10(5)mL(-1)) and more nanoflagellates (15.4 x 10(3) mL(-1)) in the mesocosm fed with a weak influent. The majority of the total microbial ATP was attributed to sedimentary bacteria, of which >96% were inactive. Heterotrophic activity and its distribution among water, epiphytic biofilm and sediment in the mesocosm wetlands were affected by availability of bacterial substrates and grazing pressure of nanoflagellates.

Abstract: Microbial degradation is the major mechanism for removal of organic carbon from woodwaste leachate in surface flow constructed wetlands. To explore the relations of microbial biomass and heterotrophic production with hydraulic and organic loading rates as well as mass reduction rates, this study examined microbial ATP concentration and leucine incorporation rate in water, epiphytic biofilm and sediment of four surface flow mesocosm wetlands fed at different hydraulic loading rates during two periods with 10× and 3× diluted woodwaste leachate. The hydraulic loading rates from 13 to 49mmd−1 had no effects on microbial biomass and heterotrophic production. The organic loading rates between 32 and 396gCODd−1 m−3 had significant, negative correlations with heterotrophic production rate and microbial biomass of sediment, and positive correlations with heterotrophic production rates of water and epiphytic biofilm. Higher organic loading yields greater substrate availability for planktonic and epiphytic bacteria, and may induce inhibitory effect on sedimentary bacteria. Microbial attachment played an important role in the establishment of epiphytic and sedimentary communities. The reduction rates for chemical oxygen demand (COD), tannin and lignin (T&L), and volatile fatty acids (VFAs) were significantly correlated to the heterotrophic production rates of water, epiphytic biofilm and sediment together. [Copyright &y& Elsevier]

Heterotrophic activities were investigated by measuring ³Hleucine incorporation to bacterial protein and 14C-glucose turnover in surface flow constructed wetlands receiving woodwaste leachate. No significant longitudinal variation was found in heterotrophic activities of bacterioplankton. An open wetland, a vegetated wetland, and a fertilized vegetated wetland were used to examine the effects of vegetation and ammonium nitrate amendment. There was not a significant difference in treatment performance among the three wetlands, except for a significant pH increase and more efficient volatile fatty acids removal in the fertilized wetland. The fertilized wetland had the highest leucine incorporation rate and shortest glucose turnover time accompanied by file lowest glucose mineralization percentage, followed by the open wetland, then the vegetated wetland. Planktonic and sedimentary bacteria contributed to the majority or the total heterotrophic activities; epiphytic bacteria played a minor role. Heterotrophic activities were influenced by the availability of nutrient, electron acceptor, and organic substrate. Water Environ. Res., 78, 671 (2066). [ABSTRACT FROM AUTHOR]

Woodwaste leachate is usually acidic, of high oxygen demand, and toxic. To prevent potential adverse impacts of the raw leachate on heterotrophic bacteria and aquatic plants, woodwaste leachate was diluted before discharge to constructed wetlands. This study compared treatment performance among four vegetated surface flow mesocosm wetlands fed with different dilutions of woodwaste leachate over a period of 12 weeks. During another period of 13 weeks, the effluent of a vegetated wetland fed with the raw leachate was further treated in a vegetated wetland and an open wetland. The highest reduction rates for chemical oxygen demand as well as tannin and lignin were achieved in the wetland fed with the raw leachate. The most diluted (6x) woodwaste leachate yielded the lowest reduction rates and highest reduction efficiencies. Up to 47 mg L-1 volatile fatty acids in influent were depleted through wetlands with a hydraulic retention time of 13 d. Vegetation made insignificant performance differences for treatment of woodwaste leachate. Chemical oxygen demand as well as tannin and lignin were further removed through the wetlands in series, though at lower reduction rates. Wetland performance for treatment of woodwaste leachate was likely regulated by dissolved oxygen concentration and availability of bacterial substrates. [ABSTRACT FROM AUTHOR]

Abstract: Four surface-flow mesocosm wetlands were operated at different hydraulic retention times during two periods to treat diluted woodwaste leachate that was acidic, of very high oxygen demand, and toxic. Temperature, dissolved oxygen, and redox potential decreased with increasing water depth. However, there was no significant vertical variation in microbial biomass. No significant development in biomass of planktonic microorganisms was found over 6 weeks of initial operation. It took <1–6 weeks for maturation of the biofilm on submerged plant surfaces and the sedimentary microbial community. Mass reduction efficiencies of chemical oxygen demand, and tannin and lignin increased significantly with hydraulic retention time when 10% leachate was fed with tap water. When a more recalcitrant influent was fed, there was a slight increase of reduction efficiency with increasing hydraulic retention time. Reduction rates increased linearly with mass loading rates up to 0.4kgm−3 d−1 chemical oxygen demand and 0.13kgm−3 d−1 tannin and lignin. Precipitation and evapotranspiration had profound impacts on the overall performance and its variability. Mass balance-based operating data of wetlands with a mature microbial community are required for proper performance assessment. [Copyright &y& Elsevier]