Abstract:
Anaerobic Digestion (AD) is often chosen as a suitable treatment for tannery wastewater (TWW)
since this waste stream is rich in organic matter. Nevertheless, the high organic load and the
presence of compounds commonly used in the leather production process and responsible for
inhibiting the biological activity (e.g. chromium and sulphide) limit the full capitalization of the
whole potential in producing biomethane from this low-cost and interesting source of renewable
energy. Pretreatment of substrates is considered by most as the solution to overcome this negative
aspect as a higher biomethane production in a shorter time is expected after that. Actually in this
study three different temperatures have been tested, in detail, 90, 80, and 70 °C, to pretreat a real
TWW prior to a mesophilic AD process conducted in a series of batch biomethane potential (BMP)
tests aimed at evaluating the optimum temperature that can result in increasing the soluble COD
content and consequently the AD performance .
After the pretreatment, the soluble COD concentration increased from a minimum of 11% to a
maximum of 80%: which resulted in an increase of the biomethane production compared with the
raw substrate. The highest temperature (90°C) investigated gave the highest increasing in soluble
COD but had a negative effect on AD process performance, as the final production of biomethane
was 178 ml CH4/g TVS, more than 4 folds less than the maximum yield of 891 ml CH4/g TVS
obtained from the sample pre-treated at 80°C where the increase in soluble COD was by 57%.
These results highlight the critical aspect of the thermal pretreatment: the increase of temperature
can enhance the biomethane production as well as reduce it, therefore the choice of the most
suitable temperature depends strongly on the characteristics of the substrate and it can be made only
through experimental tests.
