Kentsel nitelikli arıtma çamurlarının ultrasonik yöntemle ön arıtımı

Disintegration was developed as the pretreatment process of sludge to accelerate the digestion processes. Ultrasonic treatment may be a good alternative for sludge disintegration. Ultrasonic energy can be applied biological sludge to disintegrate flocs and disrupt bacterial cells? walls, and the hydrolysis can be improved, so that the rate of sludge digestion and methane production is improved1. Ultrasound treatment as sludge disintegration results in increase of chemical oxygen demand in the sludge supernatant and size reduction of sludge solids (Tiehm etal., 1997). Ultrasonic process leads to cavitation bubble formation in the liquid phase. These bubbles grow and then violently collapse when they reach a critical size. Cavitational collapse produces intense local heating and high pressure on liquid?gas interface, turbulence and high shearing phenomena in the liquid phase. Because of the extreme local conditions, OH?, HO2?, H? radicals and hydrogen peroxide can be formed. Thus, three mechanisms (hydro-chemical shear forces, thermal decomposi-tion of volatile hydrophobic substances in the sludge, and oxidizing effect of free radicals produced under the ultrasonic radiation) are responsible for the ultrasonic activated sludge disintegration (Bougrier etal., 2005; Wang etal., 2005; Riesz etal., 1985). Previous studies showed that low frequency ultrasound like 20 kHz is very effective in activated sludge disintegration, Gonze etal., 2003; Zhang etal., 2008). The effects of initial total solids content of sludge, power density, and sonication time on floc disintegration were investigated by several researchers (Chu etal., 2001; Gonze etal., 2003; Show etal., 2007; Zhang etal., 2008). Previous studies showed that low density and long duration sonication is more efficient than high density and short duration (Pham etal., 2009; Xie etal., 2009). In this work, feasibility of using an oxidative technique of ultrasonic treatment to improve anaerobic biodegradability of biological sludge was investigated. Different specific energy inputs ranged 0 to 15880 kJ/kg DS was applied to biological sludge for disintegration purpose and optimum energy input was evaluated based on disintegration degree parameter. The disintegration degree permits to evaluate the maximum level of sludge solubilization. Increase of DD is determined as the substance that can be readily used to produce methane in the anaerobic digestion (Wang et al., 2005). The disintegration degree of sonicated sludge increased with increasing specific energy in each experiment. The highest disintegration degree was achieved 9690 kJ/kg DS application; hence 9690 kJ/kgTS of supplied energy is efficient for cell lysis. Particle size of sludge is another important parameter for floc disintegration. The reduction in particle size generally allows an easier hydrolysis of solids within the sludge due to larger surface areas in relation to the particle volumes. The result is an accelerated and enhanced degradation of the organic fraction of the solid phase (Muller, 2003). Ultrasonic treatment led to change of physico-chemical characteristics of sludge. For instance, temperature increased almost linearly with increasing specific energy. In contrast, pH decreased during ultrasonic pre-treatment. The destruction of floc structure and disruption of cells results in the release of organic sludge components into the liquid phase. Thus, sludge?s supernatant characteristics were also affected the ultrasonic pre-treatment. For 9690 kJ kg-1TS, the soluble chemical oxygen demand (SCOD), dissolved organic carbon (DOC), total nitrogen (TN), total phosphorus (TP) in sludge?s supernatant increased by 340%, 860%, 716%, and 207.5%, respectively. In sludge disintegration processes organic material is transfered to the liquid phase from the solid phase. Higher solubilisation degree of volatile solids in sludge is important for the elimination of hydrolysis phase of anaerobic biodegradation further. Ultrasonic treatment induced sludge reduction due to the solubilization of total and volatile solids. The main purpose of disintegration is the elimination of hydrolysis step to accelerate the anaerobic degradation. The potential for improving anaerobic digestion through ultrasonic pre-treatment was also evaluated with biochemical methane potential (BMP) tests. BMP results obtained in this study suggest that ultrasonic pre-treatment lead to increase the anaerobic biodegradability of biological sludge. For 9690 kJ/kg TS, 44% higher methane production in pre-treated sludge was obtained comparing to the raw sludge. Protein hydrolysis was also performed successfully by ultrasonic pre-treatment even at very low ultrasonic density levels. Furthermore, CST results showed that ultrasonic pre-treatment deteriorates the filterability of biological sludge. Keywords: Anaerobic biodegradability, biological sludge, floc disintegration, ultrasonic pre-treatment.