Critically important antimicrobial resistant Enterobacteriaceae in Irish farm effluent and their removal in integrated constructed wetlands.

This study investigated the ability of Integrated Constructed Wetlands (ICWs) to remove critically important antimicrobial resistant organisms (AROs) from farm wastewater. Influent samples from the untreated farm waste and effluent samples taken at the end of the ICW system were collected monthly from four ICWs, serving four different farm types (suckler, dairy, dairy & poultry and pig). Using selective media to screen for the presence of carbapenemase resistant organisms, plasmid mediated and AmpC ß-Lactamase producing organisms (ESBL/pAmpC) and fluoroquinolone resistant organisms, a total of 82 AROs were obtained with the majority being E. coli (n = 79). Statistically significant were the differences on the number of AROs isolated from influent (higher) compared to effluent, as well as a seasonal effect, with less AROs recovered during winter in comparison to other seasons (P < 0.05). On the other hand, there was no significant differences in the recovery of AROs on different farms. The majority of isolates from each of the farms (99%) were multi drug resistant, with 65% resistant to seven or more antimicrobials. A high incidence of tetracycline, trimethoprim/sulfamethoxazole, and ampicillin resistance was common to the isolates from all four farms but there were differences in ESBL levels with 63% of the isolates recovered from Farm 4 (piggery) being ESBLs compared to 18%, 36% and 4.5% recovered from Farms 1 (suckler), 2 (dairy) and 3 (dairy & poultry), respectively. No carbapenemase producing organisms were isolated. Our results showed that ICWs are effective in removing critically important AROs from farm wastewater on all four farm types.

Economic analyses of pig manure treatment options in Ireland.

An economic analysis was performed on treatment options for pig manure in Ireland. Costs were based on a 500 sow integrated pig farm producing 10,500 m(3) of manure per year at 4.8% dry matter. The anaerobic digestion of pig manure and grass silage (1:1; volatile solids basis) was unviable under the proposed tariffs, with costs at € 5.2 m(-3) manure. Subsequent solid-liquid separation of the digestate would cost an additional € 12.8 m(-3) manure. The treatment of the separated solid fraction by composting and of the liquid fraction by integrated constructed wetlands, would add € 2.8 and € 4.6 m(-3) manure, respectively to the treatment costs. The cost analysis presented showed that the technologies investigated are currently not cost effective in Ireland. Transport and spreading of raw manure, at € 4.9 m(-3) manure (15 km maximum distance from farm) is the most cost effective option.

Meso-scale systems used for the examination of different integrated constructed wetland operations.

Meso-scale constructed wetlands have not been commonly used for the examination of interactions and operations within differently designed wetland systems. Sixteen meso-scale constructed wetland systems (4 operations with 4 replicates each) were therefore evaluated between November 2008 and June 2010. These systems were used to examine key operations identified in the literature including hydraulic loading rates, nutrient loading rates and nutrient recycling modes. The wetlands were managed in the following modes: normal, recycling, high nutrient loading and high flow rate. The designs were such that the influents could be varied at set loading rates and concentrations. The ammonia removal rates for the meso-scale integrated constructed wetland (ICW) systems were similar to other full-scale ICW systems that have been in operation in the south-east of Ireland for the past decade. These comparable results highlight the potential cost-effectiveness of these meso-scale experimental designs for the examination of novel operations for future ICW developments.

Assessment of pre-digested piggery wastewater treatment operations with surface flow integrated constructed wetland systems.

Non-point source pollution such as land-spreading of nitrogen-rich piggery wastewater poses a significant threat to surface waters. The aim was to examine the treatment of anaerobically digested piggery wastewater using four different meso-scale integrated constructed wetland (ICW) systems planted with Glyceria maxima. Four replicates were used for each system to assess differences due to nutrient loading, hydraulic loading and effluent recycling. All systems were effective in removing total organic nitrogen, ammonia-nitrogen, nitrate-nitrogen and molybdate reactive phosphorus. However, ammonia-nitrogen removal was the greatest challenge for high flow rates (>100 m(3)/ha/d). Nitrification was higher in summer than winter. Findings show for the first time that effluent recycling within ICW was beneficial to lower ammonia-nitrogen but was associated with higher operational costs. The cost-benefit ratio based on ammonia-nitrogen removal for standard, recycling, high nutrients and high flow rate treatments was 1.08:1.04:1.06:1.00. It follows that a high flow rate was only marginally more cost-effective.

Assessment of pre-digested piggery wastewater treatment operations with surface flow integrated constructed wetland systems.

Non-point source pollution such as land-spreading of nitrogen-rich piggery wastewater poses a significant threat to surface waters. The aim was to examine the treatment of anaerobically digested piggery wastewater using four different meso-scale integrated constructed wetland (ICW) systems planted with Glyceria maxima. Four replicates were used for each system to assess differences due to nutrient loading, hydraulic loading and effluent recycling. All systems were effective in removing total organic nitrogen, ammonia-nitrogen, nitrate-nitrogen and molybdate reactive phosphorus. However, ammonia-nitrogen removal was the greatest challenge for high flow rates (>100 m³/ha/d). Nitrification was higher in summer than winter. Findings show for the first time that effluent recycling within ICW was beneficial to lower ammonia-nitrogen but was associated with higher operational costs. The cost-benefit ratio based on ammonia-nitrogen removal for standard, recycling, high nutrients and high flow rate treatments was 1.08:1.04:1.06:1.00. It follows that a high flow rate was only marginally more cost-effective.