Feasibility of focused-pulsed treated waste activated sludge as a supplemental electron donor for denitrification

We evaluated the feasibility of using waste activated sludge (WAS) from a wastewater treatment plant as an internal electron donor to fuel denitrification, by increasing its bioavailability with Focused-Pulsed (FP) technology. The focused-pulsed treatment of WAS (producing FP-WAS) increased the semi-soluble chemical oxygen demand (SSCOD) by 26 times compared with the control WAS. The maximum denitrification rate of FP-WAS (0.25 g nitrate-nitrogen [NO₃^--N]/g volatile suspended solids [VSS]·d) was greater than for untreated WAS (0.05 g NO₃^--N/g VSS·d) and methanol (0.15 NO₃^--N/g VSS·d). Centrifuging out the larger suspended solids created FP-centrate, which had a rate (0.14 g NO₃^--N/g VSS·d) comparable with that of methanol. Thus, FP treatment of WAS created SSCOD, which was an internal electron donor that was able to drive denitrification at a rate similar to or greater than methanol. One trade-off of using FP-WAS for denitrification is an increase in total Kjeldahl nitrogen (TKN) loading. While FP-WAS achieved the lowest total nitrogen and NO₃^--N concentrations in the batch denitrification test, its final ammonia-nitrogen (NH3-N) concentration was the highest, as a result of the release of organic nitrogen from the FP-treated biomass; FP-centrate had less release of total soluble nitrogen. While the return of total nitrogen (TN) is small compared with the SSCOD, the effects of the added nitrogen loading need to be considered.