Sewage sludge, a waste material commonly known as biosolids, has good potential as a valuable agricultural resource, providing that its nutrient imbalances could be overcome. Sewage sludge is rich in phosphorus but low in nitrogen and potassium. Technology exists to supplement sewage sludge with mineral fertilizers, such as urea and muriate of potash as sources of nitrogen and potassium, respectively, to produce an organo-mineral fertilizer with balanced crop nutrient requirements. Here, an experimental plot trial set up in 2008 was established at Broxton, Cheshire, UK, to compare crop yield response for typical crop varieties. Crops included wheat, oilseed rape, barley, beans and forage maize, treated with conventional fertilizer and organo-mineral fertilizer. The organomineral fertilizer is a nutrient-balanced sludge-based product produced by drying digested sewage sludge cake at 80°C in a tumbling evaporator, which produces sludge granules of 3-6 mm in diameter. Analysis was carried out on soil NPK and crop yield. N use efficiency was measured to assess N uptake. Results show that there is no significant difference in crop yield between treatments over the three trial years, with the exception of one crop. This finding demonstrates that the new organo-fertilizer is as efficient as conventional fertilizers. Moreover, levels of heavy metal in soil did not exceed permissible levels. The novelty of this research lies in the fact that it is the first field scale trial of a modified sewage sludge product that has the potential to transform a hitherto waste product into a practical fertilizer product. We conclude that the organo-mineral fertilizer is a promising alternative product for sustainable agriculture.
Biosolids were applied with urea to produce a granulated organo-mineral fertiliser (OMF) for application by farm fertiliser equipment to a range of agricultural crops. The recommended rates of nitrogen, phosphate and potash were calculated for the test crops using "The Fertiliser Manual", which assesses the nutrient requirement based on previous cropping, rainfall and soil index. The OMF produced similar crop yields compared to ammonium nitrate fertiliser when applied as a top-dressing to winter wheat, forage maize and grass cut for silage in the cropping years 2010 to 2014. In 2012 the grain yield of spring barley top-dressed with OMF was significantly lower than the conventional fertiliser treatment, due to dry conditions following application. For this reason it is recommended that OMF is incorporated into the seedbed for spring sown crops and The Safe Sludge Matrix guidelines followed. The experimental work presented shows that OMF can be used in sustainable crop production systems as a source of nitrogen and phosphorus for a range of agricultural crops.
Odor control has been an important component of the operation of the Montgomery County Regional Composting Facility. After several facility improvements, which greatly reduced off-site odors, the discharge of compost process air remained the greatest source of odor impacts on the surrounding community. Thus, the WSSC assembled a research team to investigate methods of improving odor control treatment for the process air. The research team developed bench-scale tests and gas chromatographic methods that provided a better understanding of the chemical basis for odor control. Organic sulfur-containing compounds, especially dimethyl disulfide, were identified as the primary odorants in the process air. Effective removal of the reduced organic sulfides requires oxidation by sodium hypochlorite at a neutral pH. Ammonia interferes with this oxidation process and must be removed to allow effective and reliable oxidation. Hydrogen peroxide has also been used to improve oxidation and reduce chlorine odors. The removal of organic compounds has been enhanced by the use of surfactants. These findings have resulted in further full-scale improvements to the existing compost process air scrubbing system. Water Environ. Res., 64, 13 (1992).
Surface‐water and ground‐water quality were evaluated at a site before and for four years after the area was used for entrenchment of sewage sludge. The soils in the area are sandy and are underlain by a clay barrier. Depth of the water table which in most instances is above the clay barrier is from 1.0 to 13.0 m. Water samples taken from monitoring wells, two drainage tiles located along the perimeter of the sludge trenches, a catchment pond and a nearby stream were analyzed for NO3‐N, NH4‐N, and CI. Increases in Cl concentrations were detected in shallow wells within the trench site perimeter 12 months after sludge entrenchment. Chloride levels peaked approximately 18 months after entrenchment and levels declined but not to background levels four years after entrenchment. Nitrate levels increased in shallow wells located within or near the trench site perimeter at 18 months after entrenchment and peaked at 30 months. Decreases in NO3‐N occurred thereafter but had not reached background levels in some wells. Ammonium increases were also detected in wells recording Cl and NO3‐N increases but NH4‐N increases were inconsistent. Increases in Cl and NO3‐N levels were recorded in wells potentially below the trench area, but these levels were less than those recorded for wells within the trench site perimeter. The data from this study indicate that contamination of ground water by leachate from sludge trenches was within the trench site perimeter with a lesser degree of contamination recorded in wells below the trench site. The drainage tiles and clay barrier may have had a significant effect on the resulting ground‐water data, and caution is advised in extrapolating these results to other locations.
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