Siobhan N. Jordan

Utilization of spent mushroom compost for the revegetation of lead-zinc tailings: effects on physico-chemical properties of tailings and growth of Lolium perenne.

In an attempt to promote sustainable vegetation cover on metalliferous tailings, a randomized factorial greenhouse trial of six-month duration was established to determine the effect of spent mushroom compost (SMC) amendment on the physical and chemical properties of the predominantly lead/zinc tailings. The tailings originated from the surface (20-30cm) of the partially-vegetated 76ha tailings management facility (TMF), where more than nine million tonnes of pyritic metalliferous material were deposited in an unlined land impoundment. SMC was incorporated at application rates of 0, 50, 100, 200 and 400tonha(-1), with each treatment replicated 10 times and Lolium perenne sown at a rate of 200kgha(-1). The addition of SMC was beneficent as a growing medium through improvement of the structural status of the tailings and ultimately through the provision of plant nutrients and reduction in metal concentrations. However, this improvement in the structural and chemical status of the tailings is not adequate in maintaining a sustainable vegetation cover and therefore other remedial options such as introducing a capillary break on the surface of the tailings facility are necessary.

Nitrogen removal in an integrated constructed wetland treating domestic wastewater

The nitrogen (N) removal performance of a 3.25 ha Integrated Constructed Wetland (ICW) treating domestic wastewater from Glaslough village in County Monaghan, Ireland, was evaluated in this study. The ICW consists of two sludge ponds and five shallow vegetated wetland cells. Influent and effluent concentrations of two N species, namely, ammonia-nitrogen (NH3-N) and nitrate-nitrogen (NO3-N), which were measured weekly over 2 years, together with hydrology of the ICW provided the basis for this evaluation. The influent wastewater typically contained 40 mg L−1 NH3-N and 5 mg L−1 NO3-N. Concentrations of N in the ICW effluent were typically less than 1.0 mg L−1 for both species. Overall, a total load of 2802 kg NH3-N and 441 kg NO3-N was received by the ICW and a removal rate of 98.0 % and 96.9 %, respectively, was recorded. Average areal N loading rate (245 mg m−2 d−1 NH3-N and 38 mg m−2 d−1 NO3-N) had a significant linear relationship with areal N removal rate (240 mg m−2 d−1 and 35 mg m−2 d−1, respectively) for both species. The areal first-order N removal rate constants in the ICW averaged 14 m yr−1 for NH3-N and 11 m yr−1 for NO3-N. Temperature coefficients (θ) for N reduction in the ICW were lower and less than unity for NO3-N, suggesting that the variability in N removal by the ICW was marginally influenced by temperature.

Nitrogen transformations and mass balance in an integrated constructed wetland treating domestic wastewater

Nitrogen (N) transformations and removal in integrated constructed wetlands (ICWs) are often high, but the contributions of various pathways, including nitrification/denitrification, assimilation by plants and sediment storage, remain unclear. This study quantified the contributions of different N removal pathways in a typical multi-celled ICW system treating domestic wastewater. Findings showed near complete average total N retention of circa 95% at 102.3 g m⁻² yr⁻¹ during the 4-year period of operation. Variations in total N and NH4-N removal rates were associated with effluent flow volume rates and seasons. According to the mass balance estimation, assimilation by plants and sediment/soil storage accounted for approximately 23% and 20%, respectively, of the total N load removal. These were the major N removal route besides microbial transformations. Thus, the combination of plants with high biomass production offer valuable opportunities for improving ICW performance. The retrieval and use of sequestered N in the ICW sediment/soils require coherent management and provide innovative and valuable opportunities.

Adaptive neuro-fuzzy inference system for real-time monitoring of integrated constructed wetlands

Monitoring large-scale treatment wetlands is costly and time-consuming, but required by regulators. Some analytical results are available only after 5 days or even longer. Thus, adaptive neuro-fuzzy inference system (ANFIS) models were developed to predict the effluent concentrations of 5-day biochemical oxygen demand (BOD5) and NH4-N from a full-scale integrated constructed wetland (ICW) treating domestic wastewater. The ANFIS models were developed and validated with a 4-year data set from the ICW system. Cost-effective, quicker and easier to measure variables were selected as the possible predictors based on their goodness of correlation with the outputs. A self-organizing neural network was applied to extract the most relevant input variables from all the possible input variables. Fuzzy subtractive clustering was used to identify the architecture of the ANFIS models and to optimize fuzzy rules, overall, improving the network performance. According to the findings, ANFIS could predict the effluent quality variation quite strongly. Effluent BOD5 and NH4-N concentrations were predicted relatively accurately by other effluent water quality parameters, which can be measured within a few hours. The simulated effluent BOD5 and NH4-N concentrations well fitted the measured concentrations, which was also supported by relatively low mean squared error. Thus, ANFIS can be useful for real-time monitoring and control of ICW systems.

Comparing the anaerobic digestion of Ascophyllum nodosum, the organic fraction of municipal solid waste and white rice in batch reactors

The biogas potential of marine macroalga Ascophyllum nodosum was compared with the organic fraction of municipal solid waste (OFMSW) and white rice to determine the applicability of the feedstock for anaerobic digestion. For OFMSW three dry matter contents were compared, 3%, 10% and 25%, to determine the effect of dry matter on methane yield. Biogas was evolved in each system, but the rate of evolution of biogas changed with moisture content. The highest total methane yield was obtained from 3% OFMSW but A. nodosum yielded more methane at 176±37.62 L/kg VS than white rice and the drier anaerobic digestion of OFMSW. The substrates were digested using wastewater treatment plant inoculum to determine gas yield and gas quality under batch mesophilic digestion conditions.