Optimization of a thermal hydrolysis process for sludge pre-treatment

Abstract

a b s t r a c tAt industrial scale, thermal hydrolysis is the most used process to enhance biodegradability of the sludge produced in wastewater treatment plants. Through statistically guided Box-Behnken experimental design, the present study analyses the effect of TH as pre-treatment applied to activated sludge. The selected process variables were temperature (130-180 C), time (5e50 min) and decompression mode (slow or steam-explosion effect), and the parameters evaluated were sludge solubilisation and methane production by anaerobic digestion. A quadratic polynomial model was generated to compare the process performance for the 15 different combinations of operation conditions by modifying the process variables evaluated. The statistical analysis performed exhibited that methane production and solubility were significantly affected by pre-treatment time and temperature. During high intensity pre-treatment (high temperature and long times), the solubility increased sharply while the methane production exhibited the opposite behaviour, indicating the formation of some soluble but non-biodegradable materials. Therefore, solubilisation is not a reliable parameter to quantify the efficiency of a thermal hydrolysis pre-treatment, since it is not directly related to methane production. Based on the operational parameters optimization, the estimated optimal thermal hydrolysis conditions to enhance of sewage sludge digestion were: 140e170 C heating temperature, 5e35min residence time, and one sudden decompression.

Pre-treatments to enhance the biodegradability of waste activated sludge: Elucidating the rate limiting step

“…However, in other cases, higher COD solubilization did not result in a higher biogas production, but sometimes in the same or even lower biogas production (Dhar et al, 2012;Haug et al, 1978;D.-H. Kim et al, 2013;J. Kim et al, 2013b;Nazari et al, 2016;Sapkaite et al, 2017). Since COD solubilization is apparently not an accurate parameter to predict the effectiveness of subsequent biogas production (Sapkaite et al, 2017), until now, batch or (semi)continuous, anaerobic digestion methods are the only useful and accurate tools to assess the effect of pre-treatments on the anaerobic biodegradability of WAS.…”

“…Kim et al, 2013b;Nazari et al, 2016;Sapkaite et al, 2017). Since COD solubilization is apparently not an accurate parameter to predict the effectiveness of subsequent biogas production (Sapkaite et al, 2017), until now, batch or (semi)continuous, anaerobic digestion methods are the only useful and accurate tools to assess the effect of pre-treatments on the anaerobic biodegradability of WAS. In this sense, biodegradability is a characteristic of sludge, and in anaerobic digestion processes it is composed of hydrolysis rate and biodegradation extent.…”

“…Both the steam injection and the temperature increase, rise the pressure, which is suddenly released once the target values of temperature, pressure and application time are reached. In such cases, not only the effect of temperature is present but also that of the abrupt pressure drop, which increases both solubilization (Donoso-Bravo et al, 2011) and methane production (Sapkaite et al, 2017). The relevant parameters are temperature, application time, pressure, and the presence of a sudden pressure drop.…”

Thermal disinfection of hospital wastewater in a pilot-scale continuous-flow system

“…This could be related to particle breakup caused by temperature and pressure shocks inside the pilot. A similar effect is observed during thermal pressure hydrolysis of waste activated sludge where high temperature and pressure conditions are used to disintegrate and partially solubilize the sludge (Pérez-Elvira et al 2010;Phothilangka et al 2008;Sapkaite et al 2017).…”

Steam Explosion Pretreatment of Sludge for Pharmaceutical Removal and Heavy Metal Release to Improve Biodegradability and Biogas Production

“…Additionally, when the retention time was too short (i.e., 1 and 5 min) at all pressures, the pretreatment was not successful in structure breakdown or in changing the chemical structure. The conditions with the pressure and time of greater 5 bar and 5 min, respectively, had the greatest effect on the methane yield of the PS and WAS [37]. The biodegradability of pretreated primary sludge and pretreated WAS was found to increase from 29% and 25% to 80% and 71%, respectively (pretreatment at 10 bar for 15 min for sludge and 15 bar for 10 min for inoculum) ( Figure 6).…”