Evaluation of the reject waters from co-digestion of solid wastes from agro-industries in a municipal WWTP

Abstract

Overcapacities of anaerobic digesters at municipal WWTPs are frequently used for the treatment of organic wastes in order to increase the biogas production. However, "co-digestion" of organic wastes leads to additional nitrogen loading and to additional loads of non-biodegradable COD. The effects of (co-) digestion of organic wastes from agro-industries (slaughterhouses, dairies and leather industry) on the wastewater cycle have been evaluated in full-scale investigations at Leoben WWTP with a capacity of 90,000 pe where the methane production was increased from 700 to more than 1700 Nm3 CH4 per day. For this evaluation, mass balances for COD and nitrogen have been applied to estimate the fluxes of these substances. Application of this method is described in detail. As the additional loadings, it was found that related to methane production less nitrogen is released from the organic wastes than from the waste sludge. While the ammonia nitrogen load in the effluent from sludge digestion was about 100 g NH4-N per Nm3 of CH4 produced, in the effluent from the digestion of organic wastes only 70 g NH4-N/Nm3 CH4 were found. The decrease in the COD removal efficiency after digestion of the organic wastes started was not regarded as significant enough to be seen as a consequence of the treatment of external substrate.

Codigestion of solid wastes: A review of its uses and perspectives including modeling

“…Codigestion of SS with OFMSW, as well as with other wastes, increases the nutrient load of the plant. This effect was reported by Nowak et al (2007), in a paper about the WWTP in Loewen (Austria). This plant is typical of many oversized digesters in WWTP.…”

Modeling of Pollutants Removal in Subsurface Vertical Flow and Horizontal Flow Constructed Wetlands

“…In Europe, the biggest municipal and agro-industrial wastewater treatment plants (WWTPs) utilize anaerobic sewage sludge digestion with biogas production [1]. The possibility of heat and electric energy production from biogas is an advantage of such sewage sludge treatment, which decreases the cost of waste treatment significantly.…”

Co-digestion of food waste in municipal wastewater treatment plants: Effect of different mixtures on methane yield and hydrolysis rate constant

“…It is estimated that every year nearly 1.3 billion tons of food products including fresh vegetables, fruits, meat, bakery and dairy products are lost due to inefficiencies along the food supply chain and the amount will likely increase in the next 25 years due to economic and population growths, mainly in Asian countries [4]. Previous studies have already pointed to the main disadvantages of co-digestion of food waste with sludge from municipal wastewater treatment facilities including return of streams with high nitrogen load [5] and reduced dewaterability http://dx.doi.org/10.1016/j.apenergy.2014. 10.025 0306-2619/Ó 2014 Elsevier Ltd. All rights reserved.…”