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UBC Theses and Dissertations

Composting of pulp and paper mill power boiler fly ash with wastewater treatment sludge Hackett, Graydon Alexander Ross


Environmental concerns and economic realities are influencing the options available for sludge disposal from high rate wastewater treatment facilities in the pulp and paper industry. Landfilling and incineration of sludge products are no longer viable options. Composting of sludge and other waste products such as fly ash represents a way to reduce the amount of solid waste which must be disposed of. Composting produces a stabilized product that can be used as a beneficial soil amendment. Elk Falls Pulp and Paper in Campbell River, B.C., sponsored an investigation into composting wastewater treatment sludge with power boiler fly ash to produce a beneficial soil amendment. Compost was produced in windrows 50 m long, 4 m high and 6 m wide. The windrows were sampled regularly and temperature, pH, C:N ratio and moisture content were measured to monitor biological activity. Samples of the initial and final compost products were analyzed for both agronomic properties and contaminants of concern, while the process was evaluated logistically. Compost was produced in both a turned and static pile. Temperatures above 55°C for 3 weeks precluded weed growth. Moisture content was maintained above 50% to ensure microbial activity. The final compost contained high nutrient concentrations (P, K, Ca, Mg, Mn, B, Na, Al, N, S), a pH of 8.5 and an average C:N ratio of 43:1. All metal, PCB, chlorophenol and PAH concentrations were below regulated levels in British Columbia in the Contaminated Sites Regulation. The compost contained a final dioxin concentration of 41.3 pg/g TEQ. The lengthy period required to stabilize the compost (34 weeks) may have been due to N-limitation. Smallscale composter studies provided some evidence that the 1:1 sludge:ash mixture used in the large scale experiments may be N-limited. The addition of chicken manure to the mixture of raw materials improved biological activity within the compost. Leachate produced from compost of industrial wastes could potentially be hazardous and contaminate water resources. Leachate from the large scale compost piles was produced in the lab using a rigorous agitated leachate extraction test. Leachate samples were analyzed for copper, zinc, sodium, lead, nitrate, sulfate, total phosphorus, pyrene, napthalene, phenanthrene and ionic material (electrical conductivity). The leachate met all the requirements for aquatic environments according the B.C. Contaminated Sites Regulation. It is important to note that direct comparison of the leachate was made to the criteria which are specified for bodies of water after they have received all discharges. Finally, land application trials of the compost were completed at a sod farm in the Comox Valley. These experiments were completed to provide information on the fate of dioxin/fiirans once mixed with soil and to test the fertilizer qualities of the compost. Application of compost (8 yards/acre; 15m³/ha) at the sod farm improved soil characteristics as measured by a number of parameters. The dioxin concentration in the final soil/compost mixture was 3 pg/g TEQ, as compared to the agricultural soil limit of 10 pg/g TEQ. Composting produced an acceptable soil conditioner, with limited leachate concerns and such material may be attractive for large volume users of inexpensive soil material (sod farms, golf courses, land reclamation sites).

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