Field Method for Biosolids N Mineralization Using Porous Ceramic Cups

A new technique was developed for field determination of N mineralization from biosolids, which provides a simple, inexpensive test that yields accurate results. A residuals technique was used; mineralization was defined as the difference between the original and final mass of organic nitrogen. Biosolids were collected from a number of British Columbia wastewater treatment plants (WWTPs), placed in porous ceramic tubes and incubated under controlled conditions. Variables studied included wet versus dry biosolids, application rate, tube size, inoculation solution, and the effect of a soil addition mixed with biosolids. There was little difference in N mineralization between wet and dried biosolids, however variability was reduced using dried biosolids. No difference was observed using different amounts of biosolids. When dried biosolids were inoculated with supernatant obtained from a soil and biosolids mixture, decomposition was higher than with supernatant from the individual mediums alone. However, mineralization was fairly close with all inoculates. The addition of soil had little effect on biosolids decomposition other than resulting in a higher variability.