A model simulating the effluent nitrogen (N) concentration of treated animal farm wastewater in a pilot on-site constructed wetland (CW) system, using dewatered alum sludge cake (DASC) as wetland substrate, is presented. The N-model was developed based on the Structural Thinking Experiential Learning Laboratory with Animation software and is considering organic nitrogen, ammonia nitrogen (NH₃) and nitrate nitrogen (NO₃-N) as the major forms of nitrogen involved in the transformation chains. Ammonification (AMM), ammonia volatilization, nitrification (NIT), denitrification, plant uptake, plant decaying and uptake of inorganic nitrogen by algae and bacteria were considered in this model. pH, dissolved oxygen, temperature, precipitation, solar radiation and nitrogen concentrations were considered as forcing functions in the model. The model was calibrated by observed data with a reasonable agreement prior to its applications. The simulated effluent detritus nitrogen, NH₄-N, NO₃-N and TN had a considerably good agreement with the observed results. The mass balance analysis shows that NIT accounts for 65.60%, adsorption (ad) (11.90%), AMM (8.90%) followed by NH₄-N (Plants) (5.90%) and NO₃-N (Plants) (4.40%). The TN removal was found 52% of the total influent TN in the CW. This study suggested an improved overall performance of a DASC-based CW and efficient N removal from wastewater.

Denitrifying bioreactor technology, where a solid carbon source (woodchips) acts as a reactive medium to intercept agricultural tile drainage water, has been successfully used to convert N (NO3-) to di-nitrogen (N2) gas. Four replicated field-scale (24 m long × 3 m wide × 1 m deep), bioreactors were built and operated at the St. John's Research and Development Centre and were successful at removing a notable amount of nitrate (N) from agricultural subsurface drainage water. The objective of this study was to investigate the internal flow dynamics of one of these field-scale bioreactors as a proxy for the others. The hydraulic conditions in the bioreactor system developed differently than expected; asymmetric flow rates led to long average hydraulic retention time (HRT) and a highly dispersed residence time distribution, which was revealed by a sodium chloride tracer test. To measure the internal flow a known amount of sodium chloride (salt) was added to water before it entered the bioreactor and samples were collected in 30 minutes intervals. The temperature of water samples taken from the inlet, outlet, and sample ports ranged from 14.5 to 18.4°C With a N removal of 62 to 66% the bioreactor proved at the same time to be very effective under the boreal environment of Newfoundland and Labrador (NL). Mass removal rate (MRR) was calculated to evaluate the performance of woodchip bioreactor. The average MRR was 3.87 gm-3day-1 and the highest was 7.19 gm-3day-1 respectively. The theoretical retention time was calculated to be approximately 10.64 h based on the active flow volume, the length and depth of the system. In comparison the observed retention was 18.18 h.

Subsurface tile drainage installation helps to maintain water table levels and to meet adequate crop moisture requirements. Artificial subsurface drainage continues to be a common practice in Newfoundland and Labrador (NL) and elsewhere around the world. The main objective of this study was to evaluate the performance of DRAINMOD in simulating water table depth (WTD) and water outflow from tile drained agricultural fields. This site on the Avalon Peninsula of Eastern Newfoundland has a rolling landscape with predominantly Podzolic soils. The tile drainage was installed at 1.0 m deep and spaced 12 m apart. Drainage outflows (two per plot) from twelve experimental plots (32 m × 60 m each) were monitored for two years. The simulated WTD ranged from 140 cm to 160 cm during rainfall season. The performance of the model was evaluated by the Index of agreement (IOA). It was 0.600 in 2017 and 0.559 in 2018. The result was considered to have acceptable accuracy, which can help to design or evaluate subsurface drainage systems in NL, Canada. However, further evaluation including additional sites are necessary to ensure optimum drainage design parameters for the major agricultural soils.