J. Mulqueen

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.

The Performance of Fibrous Peat Biofilters in Treating Domestic Strength Wastewater

Peat is an abundant resource in Ireland and has the capacity to be used in low-cost, low-maintenance wastewater treatment systems for single houses. In this study four fibrous peat columns, of varying depths were constructed and tested in the laboratory for their capacity to remove contaminants from domestic-strength synthetic wastewater. The four filters had peat depths of 0.3 m, 0.6 m, 0.9 m and 1.2 m. During the 360 day study the filters were intermittently loaded with domestic strength synthetic wastewater at a hydraulic loading rate of 180 l/m2ċd. Hydrographs and residence times for each filter were examined as was their ability to remove impurities from the wastewater. Removal of 5-day biochemical oxygen demand (BOD5) and total chemical oxygen demand (CODt) were ≥96% and 84%, respectively, in all filters with almost complete nitrification (≥99%) being recorded for each filter. The removal of total suspended solids (TSS) was excellent at ≥94% and no clogging was recorded on any filter during the study. For the 0.6 m, 0.9 m and 1.2 m deep filters, total viable counts (TVC) were less than EU surface water directive limits for Class A2 potable water sources. The systems were cheap to construct and very easy to maintain.

Synthetic dairy wastewater treatment using a new horizontal-flow biofilm reactor.

The aim of this study was to develop a simple biological system that would be suitable for the treatment of dairy parlour wash waters. A novel horizontal-flow biofilm system was designed, constructed and tested in the laboratory for organic carbon and nitrogen removal from a synthetic dairy wastewater with average filtered chemical oxygen demand (CODf) of 2947.7 mg/L and total nitrogen (TN) of 295.5 mg/L. The novel biofilm system consisted of two reactor units one on top of the other. Each reactor unit comprised a stack of horizontal plastic sheets placed above one another that were supported and separated by vertical plastic cone frustums, which were formed in the sheets during manufacture. The wastewater was pumped onto the top sheet of the top reactor unit at hourly intervals for a 5-minute period and flowed over and back along alternate sheets down through the 2 units. The top unit had 8 plastic sheets and 25 mm high frustums to cater for heavy biofilm growth, and the bottom unit had 17 sheets and 11 mm high frustums for thinner biofilm growth. The organic loading of 57 g CODf/m2·d—based on the plan area of the system—was applied to the top reactor unit. When the reactor process reached pseudo steady-state, about 96% CODf, 71% TN and 100% ammonium nitrogen were removed. Low solids production occurred. The system was simple and easy to construct and operate.

Percolation testing and hydraulic conductivity of soils for percolation areas.

The results of specific percolation tests are expressed in terms of field saturated hydraulic conductivity (Kfs) of the soil. The specific tests comprise the Irish SR 6 and the UK BS 6297 standard tests and the inversed auger hole and square hole tests employed for the design of land drainage. Percolation times from these tests are converted to Kfs values using unit gradient theory and the Elrick and Reynolds (Soil Sci. 142(5) (1986) 308) model which takes into account gravitational, pressure head and matric potential gradients. Kfs is then expressed as the inverse of the percolation rate times a constant, in this way the percolation rate can be directly related to Kfs of the soil. A plot of Kfs against percolation rate for the Irish SR 6 and the UK BS 6297 standard tests is asymptotic at Kfs values less than 0.2 m/d and greater than 0.8 m/d. This behaviour creates difficulty in setting limits for percolation rates in standards. Curves are provided which enable Kfs values to be read off from percolation tests without the restrictions of head range currently enforced, for example in the Irish SR 6 and BS 6297 standards. Experimental measurements of percolation rates and Kfs were carried out on two sands in the laboratory and in the field on two soils. Kfs of these four materials was also measured using a tension infiltrometer and the Guelph permeameter. The saturated hydraulic conductivities (Ks) of the sands were also estimated in a falling head laboratory apparatus and by the Hazen formula. There was good agreement between the different tests for Kfs on each material. Because percolation time continued to increase significantly in consecutive tests in the same test hole while Kfs became constant, the latter is a better measure of the suitability of soils for percolation.

Organic Carbon and Ammonium Nitrogen Removal in a Laboratory Sand Percolation Filter

Abstract The on-site treatment of wastewaters from single dwellings requires simple, low maintenance systems that reduce the chemical and biochemical oxygen demand (COD and BOD respectively), ammonium-nitrogen (NH4-N), orthophosphate (PO4-P), phosphorus (P), and microorganisms to acceptable concentrations. Sand filters have the potential to achieve these reductions. In this study, a sand tank model of a percolation trench and filter was constructed in the laboratory, loaded with wastewater, and monitored for a period of 293 days. The silty sand filter was seeded for 153 days with effluent from an aerobic biofilm treatment unit. The filter was then loaded with synthetic wastewater of domestic strength for 193 days, when the average organic and hydraulic loading rates on the percolation trench were 13.33 g BOD/m2 d and 75 L/m2 d respectively. Removal rates of 90% for total COD, 99.3% for BOD5, >99% for total NH4-N, 89% for total PO4-P, and 96% for total suspended solids (TSS) were recorded during the study. No excessive clogging of the sand filter was observed. During the study very good dispersion of the wastewater over the sand filter by the percolation trench was recorded. The sand filter was simple to construct and operate and achieved excellent results.