The effect of step-feeding (untreated wastewater by-pass) on the performance of lab-scale columns simulating a hybrid vertical flow (VF)-horizontal flow (HF) constructed wetland (CW) system was studied. Step-feeding strategies have been adopted in several kinds of CW, but this is the first report about the use of step-feeding in VF + HF hybrid systems treating domestic wastewater. Applied loading rates were 7-11 g BOD/m day and 2.1-3.4 g TN/m day (overall system). Removal efficiency reached 98% TSS and COD and 99% BOD on average, whilst a 50% by-pass improved TN removal from 31 to 50%. Maximum surface nitrification rate (5.5 g N/m day) was obtained in VF unit, whilst maximum denitrification rate (1.8 g N/m day) was observed in HF unit. Referred to the overall system, maximum surface nitrification and denitrification rates were 2.2 and 1.6 g N/m day, respectively. However, potential nitrifying and denitrifying activities (batch assays) were 15.0 and 58.9 g N/m day, respectively. Even at 50% by-pass, operational conditions in HF unit (dissolved oxygen, redox, COD/TN ratio) were not suitable enough for denitrification. However, methane emissions were not observed and nitrous oxide emissions were relatively low.
Purpose
The University of A Coruña (UDC) elaborated the SOSTAUGA project, aiming to reach a higher sustainable level of its water management. SOSTAUGA defined four priority points of action: the restoration of the natural courses on the campus; the adoption of an ecological sanitation model; the sustainable management of urban runoff; and the reduction of water consumption in university facilities and activities. This paper aims to present the methodology, the actions and the results related to the reduction of water consumption and the potential for the use of endogenous resources.
Design/methodology/approach
The agents involved were the senior management of the centres, the committees of the Green Campus, the scholarship students and the Office for the Environment. Several actions have been experienced: audit of water consumption in sanitary services; flow reduction in washbasin taps by means of valve adjustment (and repair of the valves when necessary); replacement of tap aerators with other more eco-efficient ones; replacement of faucets; introduction of dual-flush (DF) in cisterns; and information to users (eco-label).
Findings
Water audit reached 68% of the total number of washbasins and tanks in the UDC. Efficient aerator installation covered 16% of taps and valve adjustment covered the further 33.5% and provided flow reduction of 42%. Another 20% of valve units required repair. The current situation in toilets combines tankless flush valves and cisterns with single flush mechanisms. The introduction of DF mechanisms was assessed and proposed. The cost of these actions was very low, as evidenced by the investment return period while showing a high potential for user awareness.
Originality/value
Both from the environmental (water saving) and from the economic and social points of view, this study shows that similar projects aimed at the efficient and rational use of water are applicable to the universities and other public and private schools, with potentially positive results on sustainability and people awareness.
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