Study Of Sewage Sludge Disintegration By High-pressure Homogenization

High-pressure homogenization (HPH) technology was applied as pretreatment to disintegrate sewage sludge. The effect of HPH treatment on characteristics of sewage sludge was investigated. Alkaline pretreatment combined with HPH was applied to promote sewage sludge disintegration. HPH pretreatment prior to anaerobic digestion of sewage sludge was investigated to improve the biogas production. The main conclusions of this study are as follows:The sludge disintegration degree (DDCOD) increased with the increase of homogenization pressure and homogenization cycle number, and decreased with the increase of sludge TS. The maximum DDCOD of43.94%was achieved at80MPa with four homogenization cycles for9.58g/L TS sludge sample. Sludge disintegration model of DDCCOD=kN0.4763P0.7324was established by multivariable linear regression, showing that the effect of homogenization pressure was more significant than that of homogenization cycle number and the value of rate constant k decreased with the increase of sludge TS. The specific energy consumption increased with DDCOD-Lower specific energy consumption was required for higher TS sludge.Organic materials in sewage sludge after HPH disintegration were transferred from sludge solids into solution, leading to sludge solid reduction and organic matters increase in sludge supernatant. The sludge TSS and VSS respectively decreased by31%and37%for the sludge sample with a total solid content (TS) of1.492%after HPH treatment at a homogenization pressure of80MPa with four homogenization cycles, and correspondingly SCOD, protein concentration, and polysaccharide concentration increased by57times,58times and18times, respectively. It had an excellent linear relationship existed between SCOD increase and VSS reduction. The energy efficiency results showed that the HPH treatment at a homogenization pressure of30MPa with a single homogenization cycle was most energy-efficient. The energy efficiency increased with sludge TS increase.A synergy effect was achieved with combined sludge disintegration of alkaline+HPH. Maximum DDCOD with combined treatment was59.26%. NaOH dosage≤0.04mol1-1, homogenization pressure≤60MPa and a single homogenization cycle were suitable for combined sludge treatment to improve sludge disintegration efficiency and to reduce alkaline dosage and energy consumption. Sludge disintegration model for combined treatment was1/1-DDCOD=0.713C0.334Pa234N0.119, showing that the effect of operating parameters on sludge disintegration followed the order:NaOH dosage> homogenization pressure> number of homogenization cycle.Combined treatment significantly increased energy efficiency, which decreased with the increase of homogenization pressure or homogenization cycle number.Fourier-transform infrared (FTIR), fluorescence excitation-emission matrix (EEM) and Ultraviolet (UV) spectroscopies were chosen to track the compositional and structural change of DOM after HPH treatment. FTIR spectra showed that the main components in DOM after HPH treatment were protein, polysaccharide and lipid compounds. The EEM fluorescence spectra showed two protein-like peaks at the excitation/emission wavelengths (Ex/Em) of225/330-340nm and275/310-335nm. A single broad shoulder representing substances with aromatic structure in the range245-270nm was found in the UV spectra of DOM for the treated sludge samples. The maximum BOD5/SCOD ratio of0.48was achieved using HPH treatment at60MPa with a single homogenization cycle. DOM characteristics were responsible for DOM biodegradation potential.HPH pretreatment disrupted the structure of sludge floes and induced the increase of SCOD, VDS, VFA, NH3-N and alkalinity concentration in sludge supernatant. HPH pretreatment prior to anaerobic digestion of sewage sludge could improve the biogas production.HPH pretreatment allowed a reduction of about10days in the retention time of sewage sludge anaerobic digestion. Compared with non-pretreated anaerobic digestion, total biogas yield, methane percentage and methane yield increased by4-25%,12-25%and18-57%, respectively using HPH pretreatment. CH4yield increment had an excellent linear relationship increase with the enhancement of VDS increment or SCOD increment. The CH4yield increment of1ml g" VSadd required0.10MJ kg-1TS of the specific energy (Es) of HPH pretreatment due to increasing homogenization pressure with a single homogenization cycle, and0.72MJ kg-1TS of Es by adjusting homogenization cycle number at60MPa. The minimum energy consumption of HPH pretreatment for unit methane increment (Em) of125J mL-1CH4increment was obtained at20MPa with a single homogenization cycle. Considering improvement of methane yield and energy efficiency, the optimum HPH operating conditions were the homogenization pressure of no more than60MPa and a single homogenization cycle.