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Coventry, United Kingdom

Butterworth E.,Cranfield University | Dotro G.,Cranfield University | Dotro G.,Wastewater Research and Development | Jones M.,Wastewater Research and Development | And 4 more authors.
Ecological Engineering | Year: 2013

A full scale comparison of a newly commissioned artificially aerated horizontal subsurface flow constructed wetland and a non-aerated bed of identical design was conducted to determine the efficacy of artificial aeration on tertiary nitrification. The works serves a population equivalent of 400; each bed is 100m2 and has a mean hydraulic loading rate of 0.27m3/m2/d. During the first 9 months of operation the wetlands received inlet loadings of NH4-N: 3.1±2.4g/m2/d, CBOD5: 2.8±2.0gO2/m2/d, chemical oxygen demand (COD): 19.4±11.2g/m2/d and total suspended solids (TSS): 6.6±5.0g/m2/d (mean±standard deviation, n=17). Results demonstrated enhanced nitrification in the aerated bed with 99% mass removal up to the maximum tested loading rate of 10.1gNH4 +-N/m2/d. In comparison, an ammonia removal of 59% was observed in the non-aerated bed up to a loading rate of 1.6gNH4 +-N/m2/d beyond which performance deteriorated. Carbonaceous biochemical oxygen demand and suspended solids removal were seen to be statistically similar between the beds while a significant difference was observed in terms of mixing pattern, quantity and characteristics of the accumulated solids and hydraulic conductivity. The suitability of the technology was also assessed through comparison of cost, carbon footprint and land area relative to alternative upgrading options. Retrofitting existing horizontal subsurface flow wetlands was shown to be the most cost effective solution delivering the required treatment at 38% of the cost of the least expensive alternatives. © 2013 Elsevier B.V. Source

Aboobakar A.,Cranfield University | Jones M.,Wastewater Research and Development | Vale P.,Wastewater Research and Development | Cartmell E.,Cranfield University | And 2 more authors.
Water, Air, and Soil Pollution | Year: 2014

Methane (CH4) formation inwastewater treatment is linked to long residence times under anaerobic conditions such as those in sewers and primary treatment units. Emissions of this methane to the atmosphere can occur under turbulent flows and, potentially, during aeration in an activated sludge plant. An online, 8-week monitoring campaign of CH4 emissions and operational conditions was conducted to study emissions froma fullscale nitrifying activated sludge plant (ASP). Significant emissions were found throughout the aerated lane, with the highest values observed two thirds down the lane. Emissions had high diurnal and spatial variability, with values ranging from 0.3 to 24 g CH4/h. No significant correlations were found between dissolved oxygen, aeration or influent loads. The results suggest that emissions are linked to upstream process conditions, with potential for methane generation in-lane due periods of limited oxygen availability. The dynamic oxygen profile observed suggests that aerobic and anoxic conditions coexist in the lane, leading to limited oxygen diffusion from the bulk liquid to the inner regions of the floc where anoxic/anaerobic layers may allow methanogenic microorganisms to survive. The average emission factor was 0.07 % of removed chemical oxygen demand, giving a total of 668 kg CH4/year and 14,000 CO2 equivalents/ year. The operational carbon associated with the energy requirements of the ASP increased by 5 %.With emerging legislation requiring the reporting of greenhouse gas emissions, the carbon impact may be significant, particularly as the industry moves towards a carbon-reducing future. Therefore, an adequate profiling of full-scale emissions is critical for future proofing existing treatment technologies. © 2013 Springer Science+Business Media Dordrecht. Source

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