Michael Rodgers

Studies of the impact of forests on peak flows and baseflows: a European perspective

Most of the scientific studies of forest impacts on stream flows have been conducted in North America. Many were primarily concerned with felling effects. These have generally found forests to be associated with reducing both peak and low flows. Their results, however, may not necessarily be directly applicable to European forests due to differences in tree species, forest management, catchment physiography and climate. Forests are a major land cover in Europe, and there are plans to promote and further expand the area of European forests. The recent droughts and floods in different parts of Europe have heightened interest in the role of forests on river flow regimes, particularly flood peak and dry weather baseflows. This paper presents the hydrological results from 28 basins across Europe sampling a wide range of forest types, climate conditions and ground conditions. The aim was to determine if forestry can have significant impacts on stream flows and to identify particularly critical situations. The findings highlighted coniferous plantations on poorly drained soils in NW Europe and eucalyptus in Southern Europe as the situations where the most marked changes to flows are likely to occur. In contrast, other forest types, and changes in forest cover at a regional scale will be likely to have a relatively small effect on peak and low flows.

Determining Phosphorus and Sediment Release Rates from Five Irish Tillage Soils

The aim of this study was to compare the nutrient and sediment releases from five Irish tillage soils, inclined at 10- and 15-degree slopes, under a simulated rainfall intensity of 30 mm h(-1) in a controlled laboratory study. Using the relationship between soil test phosphorus (STP) in the five soils and the dissolved reactive phosphorus (DRP) released in surface runoff, a runoff dissolved phosphorus risk indicator (RDPRI) was developed to identify the STP level for Irish tillage soils above which there may be a potential threat to surface water quality. The results of this study indicated that tillage soils may produce surface runoff P concentrations in excess of 30 microg L(-1) (the value above which eutrophication of rivers is likely to occur and the maximum allowable concentration of DRP in rivers under the EU Water Framework Directive, WFD) if their Morgans phosphorus (P(m)), Mehlich 3 phosphorus (M3-P), and water extractable phosphorus (WEP) concentrations exceed 9.5 mg L(-1), 67.2 mg kg(-1), and 4.4 mg kg(-1), respectively. This work reinforces the statutory agronomic based requirements of the European Communities (Good Agricultural Practice for Protection of Waters) Regulations 2009 (S.I. no. 101 of 2009). A statistical analysis showed that WEP gave the best prediction for runoff DRP.

Production of polyhydroxybutyrate by activated sludge performing enhanced biological phosphorus removal

In this study, polyhydroxybutyrate (PHB)--a biodegradable plastics material--was produced by activated sludge performing enhanced biological phosphorus removal (EBPR) in batch experiments under anaerobic, aerobic and anaerobic/aerobic conditions. Under anaerobic conditions, the maximum PHB content of the dry biomass was 28.8% by weight, while under aerobic or anaerobic/aerobic conditions, the maximum PHB content was about 50%. The PHB production rate with respect to the volatile suspended solids (VSS) was: (i) 70 mg/(g VSS)h under aerobic conditions that followed anaerobic conditions, (ii) 156 mg/(g VSS)h under anaerobic condition, and (iii) 200mg/(g VSS)h under aerobic conditions with energy also supplied from polyphosphate. A side stream, with initially anaerobic conditions for PHB accumulation and phosphorus release, and then aerobic conditions for PHB accumulation, was proposed. In this side stream, biomass with a high PHB content and a high PHB production rate could be both achieved.

Denitrification of a Nitrate-Rich Synthetic Wastewater Using Various Wood-Based Media Materials

This laboratory study examined the use of various wood materials as a carbon source in horizontal flow filters to denitrify nitrate-nitrogen (NO3-N) from a synthetic wastewater. The filter materials were: sawdust (Pinus radiata), sawdust and soil, sawdust and sand, and medium-chip woodchippings and sand. Two influent concentrations of NO3-N, 200 mg L−1 and 60 mg L−1, loaded at 2.9 to 19.4 mg NO3-N kg−1 mixture, were used. The horizontal flow filter with a woodchippings/sand mixture and an influent NO3-N concentration of 60 mg L−1, which operated over a study duration of 166 days, performed best, yielding a 97% reduction in NO3-N at steady-state conditions.

Nutrient removal from slaughterhouse wastewater in an intermittently aerated sequencing batch reactor

The performance of a 10 L sequencing batch reactor (SBR) treating slaughterhouse wastewater was examined at ambient temperature. The influent wastewater comprised 4672+/-952 mg chemical oxygen demand (COD)/L, 356+/-46 mg total nitrogen (TN)/L and 29+/-10 mg total phosphorus (TP)/L. The duration of a complete cycle was 8 h and comprised four phases: fill (7 min), react (393 min), settle (30 min) and draw/idle (50 min). During the react phase, the reactor was intermittently aerated with an air supply of 0.8L/min four times at 50-min intervals, 50 min each time. At an influent organic loading rate of 1.2g COD/(Ld), average effluent concentrations of COD, TN and TP were 150 mg/L, 15 mg/L and 0.8 mg/L, respectively. This represented COD, TN and TP removals of 96%, 96% and 99%, respectively. Phase studies show that biological phosphorus uptake occurred in the first aeration period and nitrogen removal took place in the following reaction time by means of partial nitrification and denitrification. The nitrogen balance analysis indicates that denitrification and biomass synthesis contributed to 66% and 34% of TN removed, respectively.

Use of Ochre from an Abandoned Metal Mine in the South East of Ireland for Phosphorus Sequestration from Dairy Dirty Water

Ochre found at coal mine drainage sites in the United Kingdom shows a high phosphorus (P) retention capacity with little mobilization of metals. This indicates that ochre has the potential to adsorb P from agricultural wastewaters for possible use as a fertilizer. Little research has focused on the ability of metal mine ochre to sequester P in an environmentally sustainable way. Untreated acid mine drainage from an abandoned copper-sulfur mine in the Avoca-Avonmore catchment in the south east of Ireland results in extensive low-value ochre deposition. In this study, P-amended water (50 mL) was mixed with this ochre (2.5 g) in batch experiments, and a maximum P adsorption capacity, calculated from the Langmuir equation, of between 16 and 21 g P kg(-1) was calculated. However, mobilization of heavy metals from Avoca ochre in distilled, surface, and dirty water batch experiments was observed. This mobilization may inhibit ochres use in P removal from wastewaters.

Nitrogen dynamics and removal in a horizontal flow biofilm reactor for wastewater treatment

A horizontal flow biofilm reactor (HFBR) designed for the treatment of synthetic wastewater (SWW) was studied to examine the spatial distribution and dynamics of nitrogen transformation processes. Detailed analyses of bulk water and biomass samples, giving substrate and proportions of ammonia oxidising bacteria (AOB) and nitrite oxidising bacteria (NOB) gradients in the HFBR, were carried out using chemical analyses, sensor rate measurements and molecular techniques. Based on these results, proposals for the design of HFBR systems are presented. The HFBR comprised a stack of 60 polystyrene sheets with 10-mm deep frustums. SWW was intermittently dosed at two points, Sheets 1 and 38, in a 2 to 1 volume ratio respectively. Removals of 85.7% COD, 97.4% 5-day biochemical oxygen demand (BOD(5)) and 61.7% TN were recorded during the study. In the nitrification zones of the HFBR, which were separated by a step-feed zone, little variation in nitrification activity was found, despite decreasing in situ ammonia concentrations. The results further indicate significant simultaneous nitrification and denitrification (SND) activity in the nitrifying zones of the HFBR. Sensor measurements showed a linear increase in potential nitrification rates at temperatures between 7 and 16 degrees C, and similar rates of nitrification were measured at concentrations between 1 and 20mg NH(4)-N/l. These results can be used to optimise HFBR reactor design. The HFBR technology could provide an alternative, low maintenance, economically efficient system for carbon and nitrogen removal for low flow wastewater discharges.

A pilot plant study using a vertically moving biofilm process to treat municipal wastewater.

The pilot plant study comprised the construction and monitoring of a new vertically moving biofilm system (VMBS) for treating municipal wastewater. The system operated on site for 11 months. The biofilm module in this system, consisting of high surface area plastic media, was vertically and repeatedly moved in cycles up into the air and down into the wastewater. The vertical movement of the biofilm module supplied sufficient oxygen for the removal of the organic carbon in the wastewater. The overall physical oxygen transfer coefficient (Kla) measured at the cycle speed of six cycles per minute was 2.53 per hour. During the pilot study, dissolved oxygen (DO) concentrations in the bulk fluid were in the range of 1.5-5 mg/l. It was found that the areal removal rate of filtered chemical oxygen demand (COD) was up to 35 g COD/(m(2)day) and the bulk fluid volumetric filtered COD removal rate was 2.62 kg COD/(m(3)day). The field experiment showed that clogging commonly found in other biofilm systems did not occur in this system. The power consumption was in the range of 0.09-0.25 k Wh/m(3) wastewater flow, 0.40-2.19 k Wh/kg COD removal and 1.24-1.74 k Wh/kg BOD removal. The new biofilm system offers potential for reduced reactor volumes, energy saving, simple construction and easy operation.

On-farm treatment of dairy soiled water using aerobic woodchip filters

Dairy soiled water (DSW) is produced on dairy farms through the washing-down of milking parlours and holding areas, and is generally applied to land. However, there is a risk of nutrient loss to surface and ground waters from land application. The aim of this study was to use aerobic woodchip filters to remove organic matter, suspended solids (SS) and nutrients from DSW. This novel treatment method would allow the re-use of the final effluent from the woodchip filters to wash down yards, thereby reducing water usage and environmental risks associated with land spreading. Three replicate 100 m(2) farm-scale woodchip filters, each 1 m deep, were constructed and operated to treat DSW from 300 cows over an 11-month study duration. The filters were loaded at a hydraulic loading rate of 30 L m(-2) d(-1), applied in four doses through a network of pipes on the filter surface. Average influent concentrations of chemical oxygen demand (COD), SS and total nitrogen (TN) of 5750 ± 1441 mg L(-1), 602 ± 303 mg L(-1) and 357 ± 100 mg L(-1), respectively, were reduced by 66, 86 and 57% in the filters. Effluent nutrient concentrations remained relatively stable over the study period, indicating the effectiveness of the filter despite increasing and/or fluctuating influent concentrations. Woodchip filters are a low cost, minimal maintenance treatment system, using a renewable resource that can be easily integrated into existing farm infrastructure.

Site-specific P absorbency of ochre from acid mine-drainage near an abandoned Cu-S mine in the Avoca–Avonmore catchment, Ireland

Abstract Acid mine-drainage from an abandoned Cu-S mine adit, located in the Avoca-Avonmore catchment in the southeast of Ireland, results in low-value ochre deposition. Ochre found on-site had similar physical (particle size 97.7% <2 mm and dry bulk density 0.8 g cm3), but dissimilar maximum P-retention characteristics (16-21 g P kg-1) to coal-mining ochre found in the UK. Stereomicroscopy identified oolites and diatoms in the ochre that were indicative of acidic environments. X-ray diffraction showed Fe mineralogy consisting of goethite, jarosite and minor amounts of ferrihydrite. Investigations by inductively coupled plasma-mass spectrometry and bulk energy-dispersive spectroscopy showed potentially toxic concentrations of Fe, Zn, Pb, As and Cu. Rapid mobilization of metals occurred during P-adsorption tests, which makes Avoca ochre unsuitable for use in a surface-water environmental technology.