Pre-precipitation Followed by Biological Denitrification Supported by Addition of Biological or Thermal/Chemical Hydrolysis Products

Abstract

Pilot scale experiences are reported for the process combination of pre-precipitation followed by biological nitrogen removal. Biological denitrification was supported by addition of hydrolysis products from hydrolysis of pre-precipitated primary sludge. Pre-precipitation was performed with PAX and with JKL, respectively. The biological nitrogen removal was performed based on the Bio-Denitro system. Hydrolysis products from biological sludge hydrolysis and from thermal/chemical sludge hydrolysis were applied in the experiments.

Both precipitation chemicals resulted in efficient reductions in COD, phosphorus, and suspended solids. JKL was more efficient for precipitation of phosphorus than PAX. Reduction in nitrogen was low for both chemicals. Due to the very different levels to which COD and nitrogen were reduced, the ratio of COD to nitrogen was reduced from 10–12 in the raw wastewater to 4.5–5.0 in the pre-precipitated wastewater.

Nitrogen reduction in the Bio-Denitro plant was studied with pre-precipitated wastewater alone and with pre-precipitated wastewater with addition of biological hydrolysate and various doses of thermal/chemical hydrolysate, respectively. Mean nitrogen reductions of 63% and 67% were found for the two chemicals with an influent of chemically precipitated wastewater alone. When biological hydrolysate was added, the mean nitrogen reduction was increased to 76%; with the addition of thermal/chemical hydrolysate, the mean reduction was 77%.