Successful renovation of wastewater and sludge via land application depends upon sludge-induced soil changes associated with carbon (C) and nitrogen (N) cycles within the soil/plant system. The C, N, and hydrologic cycles within a soil/sludge system receiving a year-round, daily application of paper mill sludge were studied. Soil samples were collected from three locations on a land application site in the Piedmont of Virginia that had received papermill sludge applications for six, two, and no prior years. The average application rate was 4.4 cm/wk, each week of the year, with a N loading of 700 kg N ha⁻¹yr-⁻¹. The column study showed that C and N were still accumulating on the land application site after 6 years, but at a decreasing rate. Based on this study, C accumulation will level out after 13 years of application, but N will continue to accumulate for almost 30 years. As application period increased, soil bulk density increased in the O, A, and B horizons, the percentage of non-capillary porosity fell below 10% in the A horizon and approached zero in the B horizon, and there was a dramatic decrease in the soil's hydraulic conductivity in both the A and B horizons. Nitrogen leaching is expected to increase with time due to high amounts of N in the papermill sludge, a continued narrowing of the C:N ratio, a high percentage of nitrification, and low denitrification rates. Experimental timing and rates of sludge additions were imposed to alter the aerobic/anaerobic properties of the soil system to determine the conditions under which optimum C and N mineralization, nitrification, and denitrification would occur. Application rates were factorially arranged for single or multiple doses on a daily or alternating schedule. The C decomposition and N mineralization processes were both optimized with an increase in the length of cycle; they were maximized with an alternating 9 days on/9 off application schedule. The nitrification potential also increased with the length of cycling, with an average nitrification rate of 96%. Denitrification was minimal in all treatments, with an average denitrification rate of 16%. This was primarily attributed to movement of nitrate-N below the most biologically active zone in the soil column. Sludge renovation will ultimately depend upon the excess N being sequestered in plant biomass or denitrified. Proper management of these processes will ensure that wastes decompose, and that N is stored or evolved as a benign gas rather than leached at unacceptable levels. / Master of Science

Coliform bacteria have long been used to indicate fecal contamination of food, water, and solid surfaces, and thus the presence of a health hazard. In this study, the in-mill water and external effluent treatment systems of seven typical Canadian pulp and paper mills were shown to support the growth of numerous coliforms, especially Klebsiella spp, Escherichia coli, Enterobacter spp., and Citrobacter spp . Mill coliforms were shown to be not just simple transients from feedwater or furnish (wood), but to be continuously growing, especially in the primary clarifiers. Therefore, coliforms and fecal coliforms cannot be used as fecal contamination indicators in pulp and paper mill water and effluent treatment systems. / N2-fixing coliform populations were detected in mill water systems and were analyzed using N2-fixation assays and nitrogenase gene (nifH) probing. Both active in situ populations and cultured microbial isolates were tested. Active N2-fixation was demonstrated in six primary clarifiers. Measurement of the numbers and composition of the total culturable bacterial community in a primary clarifier revealed that approximately 50% of all aerobic cells contained nifH , of which >90% were Klebsiella. Coliforms growing on MacConkey agar plates from the primary clarifier were all identified as Klebsiella and 100% of these Klebsiella contained the nifH gene. Preliminary estimates indicate that the amount of N2 fixed per day is substantial in some clarifiers.

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