Main Pathways in Primary Sludge Disintegration by Sonication and Enhancement of Sonication

The main pathways of primary sludge(PS)ultrasonic disintegration were analyzed at the sonication frequency of 20 kH z and the thermal effect on PS disintegration was investigated.By adding Na HCO3as a scavenger to entrap the free hydroxyl radicals,cavitation contributed to 82.91%of the total sonication effect.The power consumed by temperature rising accounted for more than40%of ultrasound power input at the power density of 0.215 W/m L and the sonication time of 10 min.With the thermal insulation of polyfoam coating during sonication,a 18.37%of soluble chemical oxygen demand(SCOD)increment was observed.With the process of pre-heating the PS before sonication,64.15%of SCOD increment was achieved.Compared with the particle size of 13.77μm for the sonicated PS,the sludge mean particle size decreased to 12.83 and11.98μm by applying polyfoam coating and pre-heating the PS to enhance the cavitation and thermal effect.It suggested that if thermal energy consumption was relieved during the sonication process of PS,more energy could be used to disintegrate the sludge.

Sewage sludge disintegration by high-pressure homogenization: A sludge disintegration model

High-pressure homogenization （HPH） technology was applied as a pretreatment to disintegrate sewage sludge. The effects of homogenization pressure, homogenization cycle number, and total solid content on sludge disintegration were investigated. The sludge disintegration degree （DDCOD）, protein concentration, and polysaccharide concentration increased with the increase of homogenization pressure and homogenization cycle number, and decreased with the increase of sludge total solid （TS） content. The maximum DDCOD of 43.94% was achieved at 80 MPa with four homogenization cycles for a 9.58 g/L TS sludge sample. A HPH sludge disintegration model of DDCOD= kNaPb was established by multivariable linear regression to quantify the effects of homogenization parameters. The homogenization cycle exponent a and homogenization pressure exponent b were 0.4763 and 0.7324 respectively, showing that the effect of homogenization pressure （P） was more significant than that of homogenization cycle number （N）. The value of the rate constant k decreased with the increase of sludge total solid content. The specific energy consumption increased with the increment of sludge disintegration efficiency. Lower specific energy consumption was required for higher total solid content sludge.

Waste sludge disintegration, methanogenesis and final disposal via various pretreatments: Comparison of performance and effectiveness

This study compared the three wastewater pretreatments of ozonation,Fe2þ-S2O82and freeze-thawing(F/T)in the disintegration,anaerobic digestion(AD)and final disposal of the sludge.The F/T pretreatment increased the dewaterability and settleability of the sludge by 7.8%and 47.1%,respectively.The ozonation pretreatment formed more volatile fatty acids(VFAs),with a peak value of 320.82 mg SCOD/L and controlled the release of sulfides.The Fe2þ-S2O82pretreatment removed heavy metals through the absorption and flocculation of ferric particles formed in-situ.During the anaerobic digestion of the sludge,the ozonation pretreatment accelerated the hydrolysis rate(k)rather than the biochemical methane potential(B0)of the sludge due to the high VFA content in the supernatant.Comparatively,the F/T pretreatment facilitated the B0 with great economic efficiency by enhancing the solubilisation of the sludge.Although Fe2þ-S2O82pretreatment decreased the methane production,the ferric particle was a unique advantage in the disintegration and harmless disposal of the sludge.The digested sludge had more VFAs after ozonation pretreatment,which contributed to the recycling of carbon.In addition,the lower sludge volume could save the expense of transportation and disposal by ozonation pretreatment.Different pretreatments had different characteristics.The comparative study provided information allowing the selection of the type of pretreatment to achieve different objectives of the treatment and disposal of sludge.

Compared effects of “solid-based” hydrogen peroxide pretreatment on disintegration and properties of waste activated sludge

The effects of two solid-based hydrogen peroxides sodium percarbonate(SPC) and calcium peroxide(CP)on waste activated sludge(WAS) disintegration were investigated. Both oxidants achieved efficient WAS disintegration for the synergistic effect of alkaline and oxidation. The strong alkaline condition led to the leakage of ammonia and the existence of abundant calcium ions accelerated the fixation of phosphorus via precipitation in CP WAS disintegration process. However, the spongy-like layer and low p H condition retarded the release of gaseous ammonia in SPC group. Hydroxyl radical was the main oxygen reactive species in SPC approaches which were more intense than CP by electron spin resonance(ESR) analysis.CP treated WAS contented more small particle size matter and total suspended solids(TSS) increased dramatically. In conclusion, CP pretreated sludge was more suitable for fertilization, while SPC was in favor of anaerobic digestion. This study clarified the differences between these two oxidants and their intermediates on nutrients release in sludge disintegration.

Enhancement of ultrasonic disintegration of sewage sludge by aeration

Sonication is an effective way for sludge disintegration,which can significantly improve the efficiency of anaerobic digestion to reduce and recycle use of sludge.But high energy consumption limits the wide application of sonication.In order to improve ultrasonic sludge disintegration efficiency and reduce energy consumption,aeration was introduced.Results showed that sludge disintegration efficiency was improved significantly by combining aeration with ultrasound.The aeration flow rate,gas bubble size,ultrasonic density and aeration timing had impacts on sludge disintegration efficiency.Aeration that used in later stage of ultrasonic irradiation with low aeration flow rate,small gas bubbles significantly improved ultrasonic disintegration sludge efficiency.At the optimal conditions of 0.4 W/m L ultrasonic irradiation density,30 m L/min of aeration flow rate,5 min of aeration in later stage and small gas bubbles,ultrasonic sludge disintegration efficiency was increased by 45% and one third of ultrasonic energy was saved.This approach will greatly benefit the application of ultrasonic sludge disintegration and strongly promote the treatment and recycle of wastewater sludge.

An executive review of sludge pretreatment by sonication

Ultrasonication（US）, which creates hydro-mechanical shear forces in cavitation, is an advanced technology in sludge pretreatment. However, there are many factors affecting the efficacy of cavitation and ultrasonication disintegration of sludge as a consequence.The objective of this work is to present an extensive review of evaluation approaches of sludge US pretreatment efficiency. Besides, optimization methodologies of related parameters,the differences of optimum values and the similarities of affecting trends on cavitation and sludge pretreatment efficiency were specifically pointed out, including ambient conditions,ultrasonic properties, and sludge characteristics. The research is a prerequisite for optimization of sludge US pretreatment efficiency in lab-scale and practical application. There is not-yet a comprehensive method to evaluate the efficiency of sludge US pretreatment, but some main parameters commonly used for this purpose are degree of sludge disintegration, proteins,particle size reduction, etc. Regarding US parameters, power input PUS, intensity IUS, and frequency FSseem to have significant effects. However, the magnitude of the effect of PUSand probe size in terms of IUShas not been clearly detailed. Investigating very low FSseems interesting but has not yet been taken into consideration. In addition, static pressure effect has been marginally studied only and investigation on the effect of pH prior to US process has been restricted. Their effects therefore should be varied separately and simultaneously with other related parameters, i.e. process conditions, ultrasonic properties, and sludge characteristics, to optimize sludge US pretreatment process.