TY - JOUR

T1 - Increased retention of available nitrogen during thermal drying of solids of digested sewage sludge and manure by acid and zeolite addition

AU - Liu, Jingna

AU - de Neergaard, Andreas

AU - Jensen, Lars Stoumann

PY - 2019/12/1

Y1 - 2019/12/1

N2 - Thermal drying is an increasingly common post-treatment for digestate-solids, but prone to N losses via ammonia (NH3) volatilization. Acidification with strong acids prior to drying may retain ammonium (NH4 +) in the solids. Natural zeolites can provide adsorption sites for exchangeable cations as ammonium and porosity for free ammonia, which has the potential to contribute to higher N retention in the dried solids. The present study investigated whether the zeolite addition increases NH4 +-N retention during thermal drying of two digestate solids (manure based, MDS; sewage sludge based, SDS), and whether any synergistic effects of combining acidification with sulfuric acid and the addition of zeolite exist. Operating conditions included four pH levels (non-acidified control, adjusted to 8.0, 7.5, 6.5 with concentrated sulfuric acid), four zeolite addition rates (0%, 1%, 5% and 10%), fixed drying temperature (130 °C) and fixed air ventilation rate (headspace exchange rate of 286 times hour−1). Zeolite addition significantly increased NH4 +-N retention from 18.0% of initial NH4 +-N in the non-acidified control up to a maximum of 57.4% for MDS, and from 76.6% to 94.5% for SDS. No positive synergistic effect between acidification and zeolite addition was observed, with acidification being the dominant. Nevertheless, zeolite has the potential to be a safe and easy-to-handle alternative to concentrated sulfuric acid.

AB - Thermal drying is an increasingly common post-treatment for digestate-solids, but prone to N losses via ammonia (NH3) volatilization. Acidification with strong acids prior to drying may retain ammonium (NH4 +) in the solids. Natural zeolites can provide adsorption sites for exchangeable cations as ammonium and porosity for free ammonia, which has the potential to contribute to higher N retention in the dried solids. The present study investigated whether the zeolite addition increases NH4 +-N retention during thermal drying of two digestate solids (manure based, MDS; sewage sludge based, SDS), and whether any synergistic effects of combining acidification with sulfuric acid and the addition of zeolite exist. Operating conditions included four pH levels (non-acidified control, adjusted to 8.0, 7.5, 6.5 with concentrated sulfuric acid), four zeolite addition rates (0%, 1%, 5% and 10%), fixed drying temperature (130 °C) and fixed air ventilation rate (headspace exchange rate of 286 times hour−1). Zeolite addition significantly increased NH4 +-N retention from 18.0% of initial NH4 +-N in the non-acidified control up to a maximum of 57.4% for MDS, and from 76.6% to 94.5% for SDS. No positive synergistic effect between acidification and zeolite addition was observed, with acidification being the dominant. Nevertheless, zeolite has the potential to be a safe and easy-to-handle alternative to concentrated sulfuric acid.

KW - Acidification

KW - Ammonia loss

KW - Clinoptilolite

KW - Digestate

KW - Sulfuric acid

UR - http://www.scopus.com/inward/record.url?scp=85072733063&partnerID=8YFLogxK

U2 - 10.1016/j.wasman.2019.09.019

DO - 10.1016/j.wasman.2019.09.019

M3 - Journal article

C2 - 31574459

AN - SCOPUS:85072733063

VL - 100

SP - 306

EP - 317

JO - Waste Management

JF - Waste Management

SN - 0956-053X

ER -