Control of denitrification in a septage-treating artificial wetland: the dual role of particulate organic carbon

• Published in: Water research (Oxford) 2002-10, Vol.36 (17), p.4415-4427
• Main Authors: Hamersley, M.Robert, Howes, Brian L
• Format: Article
• Language: English
• Subjects: Anaerobic microsites; Anaerobiosis; Applied sciences; Artificial wetlands; Bacteria - metabolism; Biological and medical sciences; Biological treatment of waters; Biomass; Biotechnology; Carbon - metabolism; Cell Respiration; Denitrification; Environment and pollution; Eukaryota - metabolism; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General purification processes; Industrial applications and implications. Economical aspects; Models, Theoretical; Nitrates - metabolism; Nitrogen; Nitrogen - metabolism; Organic Chemicals - metabolism; Particulate organic carbon; Plants - metabolism; Pollution; Septage; Wastewaters; Water Pollutants, Chemical - metabolism; Water Purification; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/S0043-1354(02)00134-3

We examined the factors controlling organic carbon (C) cycling and its control of nitrogen (N) removal via denitrification in an aerated artificial wetland treating highly concentrated wastewater to nutrient-removal standards. Processing of organic material by the septage-treating wetland affected the biological reactivity (half-life, or t 1/2) of organic C pools through microbial degradation and gravity fractionation of the influent septage. Primary sedimentation fractionated the initial septage material ( t 1/2=8.4 d) into recalcitrant waste solids ( t 1/2=16.7 d) and highly labile supernatant ( t 1/2=5.0 d), allowing this reactive fraction to be further degraded during treatment in aerobic wetland tanks until a less labile material ( t 1/2=7.3 d) remained. Organic C contributions from in situ fixation by nitrifying bacteria or algae in these tanks were small, about 1% of the C degradation rate. In the aerated tanks, denitrification was correlated with particulate organic C loading rates, although the average C required (0.35 mg C L −1 h −1) to support denitrification was only 12% of the total C respiration rate (2.9 mg C L −1 h −1). Additions of plant litter (2.5 g C L −1) to the aerated tanks under normal operating conditions doubled denitrification rates to 0.58 mg N L −1 h −1, and reduced effluent nitrate levels by half, from 12.7 to 6.4 mg N L −1. However, C degradation within the plant litter (0.15 mg C L −1 h −1) was sufficient to have accounted for only 35% of the additional denitrification. Evidence from laboratory and full-scale plant litter additions as well as process monitoring indicates that the stimulation of denitrification is due to the respiration-driven formation of anaerobic microsites within particulate organic C. In this aerated highly C-loaded septage-treating wetland, anaerobic microsite, rather than C substrate availability limits denitrification.