Anaerobic treatability of liquid residue from wet oxidation of sewage sludge

Abstract

Wet Oxidation (WO) of sewage sludge is a chemical oxidation of sludge at high temperatures and pressures by means of an oxygen-containing gas. The liquid stream originated by WO is easily biodegradable, and therefore, the recirculation to the biological Waste Water Treatment Plant (WWTP) may be a feasible solution. However, the WO effluent has a residual organic and nitrogen content so that its treatment may be required when the receiving WWTP has no surplus treatment capacity left. The aim of this research was the assessment of the anaerobic treatability of the WO liquid residue, in order to reduce the organic load to be recirculated to the WWTP, simultaneously promoting energy recovery. For this purpose, the liquid residue obtained during full scale WO tests on two different types of sludge was submitted to anaerobic digestion in a continuous flow pilot reactor (V = 5 L). Furthermore, batch tests were carried out in order to evaluate possible inhibition factors. Experimental results showed that, after the start-up/acclimation period (~130 days), Chemical Oxygen Demand (COD) removal efficiency was stably around 60% for about 120 days, despite the change in operating conditions. In the last phase of the experimental activity, COD removal reached 70% under the following treatment conditions: Hydraulic Retention Time (HRT) = 20 days, Volumetric Organic Loading Rate (VOLR) = 0.868 kg COD/m(3)/day, Organic Loading Rate per Volatile Suspended Solids (OLRvss) = 0.078 kg COD/kg VSS/day, temperature (T) = 36.5 °C, pH = 8. Energy balance calculation demonstrated anaerobic treatment sustainability.

Enhanced Versus Conventional Sludge Anaerobic Processes: Performances and Techno‐Economic Assessment

“…In order to reduce the energy requirements of the WO process, anaerobic digestion of the liquid residue (rich in biodegradable COD) was proposed and tested by Bertanza et al (2014b).…”

Formation and Degradation of Soluble Biopolymers during Wet Oxidation of Sludge

“…Although the research effort on hydrothermal treatments of sludge has been substantial, these works have mainly focused on VSS, COD or TOC reductions, but none of them have attempted to characterize the reaction products, even though this information will be critical to the design of subsequent techniques of purification or revalorisation of the hydrolyzed and oxidized effluent. 20 Therefore, the aim of this work was to analyze the effect of WO on the main species of polymeric substances from activated sludge. To this end, the sludge was separated into its components (SMP, LB-EPS, TB-EPS and naked cells) in order to check the differences during treatment according to the origin of the biopolymers (extracellular or intracellular), and each was subjected to WO.…”

“…Nevertheless, to the best of our knowledge, the impact of WO on polymeric substances from sludge is still unknown. Although the research effort on hydrothermal treatments of sludge has been substantial, these works have mainly focused on VSS, COD or TOC reductions, but none of them have attempted to characterize the reaction products, even though this information will be critical to the design of subsequent techniques of purification or revalorisation of the hydrolyzed and oxidized effluent . Therefore, the aim of this work was to analyze the effect of WO on the main species of polymeric substances from activated sludge.…”

Wet Oxidation of Fine Soil Contaminated with Petroleum Hydrocarbons: A Way towards a Remediation Cycle

“…In addition, the WO effluent can be conveniently treated in a conventional wastewater treatment plant because of its high biodegradability, and, in some cases, it could also be used as a carbon source for the denitrification process, and as a substrate for the production of biopolymers [12]. Moreover, other researchers have also demonstrated that WO effluent represents an interesting energy vector; in fact, if it is treated by anaerobic digestion, biogas can be produced, and electric and thermal energy could be recovered [13].Today, about 200 plants are in operation around the world (two of them in Italy), mostly to treat waste streams from petrochemical, chemical, and pharmaceutical industries, as well as residual sludge from urban wastewater treatment [12]. Detailed reviews about the WO process and its application are reported in Debellefontaine and Foussard [8], and Bhargava et al [14].According to Italian regulations [15], the soil and stones not containing dangerous substances (classified using the European Waste Code 17 05 04 [16]) can be recovered, in simplified procedure, for the following uses: ceramic and brick manufacturing processes, environmental recovery, road embankments, and foundations.…”

“…In addition, the WO effluent can be conveniently treated in a conventional wastewater treatment plant because of its high biodegradability, and, in some cases, it could also be used as a carbon source for the denitrification process, and as a substrate for the production of biopolymers [12]. Moreover, other researchers have also demonstrated that WO effluent represents an interesting energy vector; in fact, if it is treated by anaerobic digestion, biogas can be produced, and electric and thermal energy could be recovered [13].…”