Impact of aeration on the removal of organic matter and nitrogen compounds in constructed wetlands treating the liquid fraction of piggery manure

The increasing demand for sustainable, robust and cost-efficient wastewater treatment techniques strengthen the implementation of constructed wetlands (CWs) in the agricultural sector. In countries like Belgium (Flanders), the compliance of strict water quality standards and surface area requirements have hindered considerably their application. New wetland designs such as aerated CWs, could help to overcome these challenges. This study evaluated the capacity of artificially aerated mesocosm systems to decrease chemical oxygen demand (COD) concentrations below the 125 mgO(2)/L limit imposed on installations treating animal manure. The treatment of this high-strength wastewater has been slightly studied via aerated CWs. A three-stage experiment investigated the effect of constant, intermittent and non-aeration regimes on: ammonium volatilisation, the evolution of organic and nitrogen compounds concentrations, and denitrification. The results were assessed through a mixed modelling procedure using SAS 9.4 software. A COD removal between 65% and 58% in constantly and intermittent aerated systems, versus 27% COD removal in the non-aerated system indicated the effectiveness of aeration. However, a dissimilarity was encountered in the removal of nitrogen compounds, resulting in an 82% decrease of nitrate concentrations in the non-aerated system, versus 0.5% and 11% in the aerated ones. Based on the results, this experimental set-up adjusted to field operational conditions can prove that aerated CWs can treat the liquid fraction of piggery manure

Effect of carbon dosing on denitrification in an aerated horizontal subsurface flow constructed wetland used for effluent polishing

Aerated wetlands (AW) are normally used for high oxygen demand situations and were proven optimal for nitrification. However, denitrification remains a concern in AWs especially due to unfavorable oxygen concentrations and lack of biodegradable organic matter (OM). In this study, a 350 m² aerated horizontal subsurface flow constructed wetland (HSSF CW) treating the effluent of a municipal wastewater treatment plant, was tested in a high hydraulic loading rate situation (0.69 m3.m-2.d-1, 12 hours hydraulic retention time), in combination with external carbon dosing to promote denitrification. Forced bed aeration (FBATM) allowed to independently aerate three equally sized zones along the flow direction, and was controlled by a Dissolved Oxygen (DO) sensor in each zone. Zone 1 was destined for nitrification (DO = 2-3 mg.O2.L-1), zone 2 for denitrification (no aeration) with the addition of a carbon source (Brenntaplus VP-1), and zone 3 was again aerated (DO = 2-3 mg.O2.L-1) to degrade any residual OM. Four different carbon dosages (COD/N 0, 2.0, 3.5 and 4.0) were applied at the start of zone 2, based on online measured nitrate data. The results revealed that nitrification remained optimal (±100 %) throughout the experiment despite the lower water temperature (10-15 °C). Total nitrogen (TN) removal increased from 23 to 59% as the COD/N ratio increased from 0 to 4. However, the COD removal efficiency remained moderate during initial dosing (21 and 18% for COD/N = 0 and 2, respectively) and further decreased with higher carbon dosing (no removal for COD/N = 4.0). The outcomes of this study can be helpful for implementing carbon dosing to enhance nitrate removal in full-scale AWs used for tertiary treatment

Evaluation of a new approach for swine wastewater valorisation and treatment : a combined system of ammonium recovery and aerated constructed wetland

Nitrate Vulnerable Zones (NVZs) are faced with a surplus of animal manure due to intensive livestock produc-tion, and the high use of mineral nitrogen (N) fertilisers in crop production. Recovery of N from animal manure to replace synthetic mineral fertilisers is considered a key strategy to close the N loop for more sustainable agriculture and to meet strict legal frameworks. In this study, N recovery from swine wastewater by an ammonia (NH3) stripping process followed by purification via an aerated constructed wetland (ACW) was proposed as an alternative approach to conventional systems based on biological nitrification-denitrification (NDN) treatment. The performance of the NH3 stripping pilot as well as the ACW was monitored in 2019-2020 over three periods, to evaluate the quality of recovered ammonium nitrate (AN) solution and the effluent of the ACW. Results showed that the NH3 stripping unit recovered 21% of total-N (32% of mineral-N) in the form of AN solution. This could be used as a mineral fertiliser according to the criteria of the European Fertilising Products Regulation 2019/1009 and the technical proposal of manure-derived RENURE (REcovered Nitrogen from manURE) prod-ucts by the European Joint Research Centre. As a RENURE product, AN solution would reach an end-of-manure status and could be used as a synthetic N fertiliser replacement. The tested ACW achieved a high removal ef-ficiency with respect to suspended solids (96%), biological oxygen demand (96%), chemical oxygen demand (90%), total-N (80%), and total phosphorus (97%). The quality of ACW effluent was comparable to that of NDN treatment. Though the overall cost of the proposed pilot-scale process consisting of NH3 stripping (5.1 euro t-1) and ACW (12 euro t-1) was calculated slightly higher than conventional NDN treatment (16 euro t-1), it is foreseen to outcompete at a higher loading rate (over 45 m3 ha-1 d-1). Furthermore, post-purification will be needed for the ACW effluent to meet the requirements for discharge to surface water