Preparation Of Bioflocculant With Sewage Sludge And Its Performance Analysis

With the improvement of environmental standards, shortcomings of traditional sludge treatment methods gradually appeared. Therefore, the reclamation of sludge has become an effective way to solve the problem of sludge disposal. Sludge is mainly composed of intracellular and extracellular proteins, polysaccharides and other organic matters. The proteins and polysaccharides excreted outside the cell were the active substances of bioflocculants prepared by traditional fementation method. Based on considertaion of resource reclamation, this study applied sludge as a raw material for preparing bioflocculant and provided a new way for the bioflocculant preparation.Flocculant preparation method was determined by comparing the flocculating activity of hydrolysates under different conditions. The activities and physicochemica properties of the prepared bioflocculant and its byproduct were characterized. And the flocculating mechanism was investigated. The following findings were made:(1) Hydrolysising sludge using ultrasound technology to study the effects of different ultrasonic conditions on performance.With the increase of ultrasonic density and time, the hydrolysis degree increased, but energy efficiency reduced. Impact factors of ultrasonic density and time were0.2294and0.2893, respectively. When ultrasonic energy input (the product of ultrasonic density and duration of action) was the same, whispered energy density, long duration of action was more conducive to the sludge hydrolysis.(2) Combined technology (alkaline+ultrasonic) was helpful to improve sludge disintegration. The disintegration kinetic model was established by the multi-variable linear regression method. Impact factors of independent variablessuch as pH, ultrasonic density, ultrasonic intensity and sludge concentration were2.1109、1.3933、0.8145and0, respectively. The impacting degree of factors on the sludge hydrolysis was as followed, sludge pH> ultrasonic density> ultrasonic intensity> sludge concentration, which provided a theoretical basis for sludge alkaline hydrolysis.(3) The flocculating activities of hydrolysis products under different condations were examined. It was shown that alkaline hydrolysis product had the largest flocculating activity, followed by alkaline+ultrasonic treating product, whereas of ultrasonic alone hydrolysis product possessed the poorest flocculating activity. According to this conclusion, experiments were carried out by alkaline hydrolysis. The optimized condations were determined as: hydrolysis temperature70℃, reaction time30minutes, the alkali dosage of1.75g/gTS. Under these condations, the hydrolysate was named as flocculant FM-1.(4) The orthogonal experiment showed that flocculant FM-1had the flocculating activity of98.8%on Kaolin solution (5g/L). As long as the active flocculation substances were distributed in the liquid phase, and the storage stability was poor. Thus flocculant FM-1was centrifuged, the centrifugal supernatant was called flocculant FM-2which had the flocculating activity of99.2%on Kaolin solution. FM-2also had better storage stability and thermal stability. The main components of flocculant FM-2were protein and polysaccharide, with mass fractions of70.3%and21.6%, respectively. According to the infrared scan results, it might contain hydroxyl (-OH), amino (-NH-) and ester (-COOC-) groups. Scanning electron micrograph of flocculant FM-2displayed that the geometrical appearance was round-like, particle size was relatively uniform, and the particles were intertwined, mutual adhesion. Both "compression of electric double layer theory" and "bridging theory" could explain the effects of FM-2on kaolin particles.(5) Flocculant FM-2also could be used as an agent in the wastewater treatment. FM-2functional groups were protonated under acidic condition, so it became conducive to the adsorption of anionic dye.The decolorization rates of direct turquoise blue reached99.3%. For starch wastewater with certain turbidity, the best flocculation rate was75.2%. For the practical domestic wastewater, the maximum flocculating rate was97.7%. Heavy metal element could also be removed. FM-2had better effect on the removel of selenium and lead element, with removal rate higher than90%. It also had different degree of removal on mercury, arsenic and cadmium element.(6) As a byproduct of flocculant FM-2preparation, AM-l’s adsorption of methylene blue was researched. For the initial concentration of methylene blue solution100mg/L, the equilibrium adsorption capacity was more than100mg/g when the solution pH value varied from3to11. AM-1on the adsorption behavior of methylene blue was in good agreement with Langmuir model and Freundlich model. The fitting results of1/n=0.32indicated that it belonged to the category of easy adsorption.