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Different kinds of pretreatments have been practiced to disrupt sewage sludge and release extracellular polymeric substances of sludge flocs and inner constituents of bacteria cells for efficient biochemical conversion and biogas production. Among them high pressure homogenization (HPH) is a promising unconventional mechanical pretreatment method. HPH pretreatment works on the principles of turbulence, cavitation and shearing, solubilizing the sludge or enlarging its surface area for enzymatic attack, so that enzymatic hydrolysis can be efficiently enhanced and subsequently biogas production can be significantly improved. HPH pretreatment of sewage sludge is not only investigated in research work (theoretically), but also it has been integrated into sewage sludge treatment in wastewater treatment plants, presenting positive results. However, there is still research gaps in terms of efficiency improvement and cost minimization. This review paper outlines promising aspects of sludge HPH pretreatment for biogas production enhancement and presents directions for future researches to fulfill the research gaps. [ABSTRACT FROM AUTHOR]

To improve the efficiency of sewage sludge conditioning, modified coal fly ash (MCFA) was introduced into the sludge conditioning with cationic polyacrylamide (CPAM). Specific resistance to filtration (SRF), net sludge solid yield (YN), modified filter cake moisture (FCMm), and time to filter (TTF) were analyzed to evaluate the sludge filterability and dewaterability. Results showed that the MCFA addition significantly promoted the sludge filterability and dewaterability, compared with the single CPAM conditioning. There was a synergistic effect between the MCFA and CPAM conditioning. The suitable dosages of the CPAM and MCFA were 1.3 g kg−1 and 60% DS for the experimented sewage sludge, respectively. Under the suitable conditions of dual conditioning, the YN of sludge conditioned increased by 383%, and the TTF reduced by 427 s, compared with that of raw sludge; the FCMm of sludge conditioned was 82.9%. The change in zeta potential and floc size of sludge particles after conditioning suggested that the dual conditioning improved the sludge filterability and dewaterability mainly because of the interactions between sludge and MCFA, CPAM. [ABSTRACT FROM AUTHOR]

In this study, activated carbon (AC) was prepared from municipal sludge with peanut shell as the carbon additive and the ferric chloride as activator. Then the properties of AC activated by ferric chloride (FAC) and non-activated (NAC) were analyzed. Main results show that FAC has extremely higher BET surface area (781.5 m²/g) and pore volume (0.859 m³/g) than NAC, which implies that ferric chloride can effectively promote the formation of developed pore structures of AC. Moreover, the obtained ACs were used as adsorbent to remove phenol in aqueous solution. Results indicate that FAC and NAC have a higher adsorption capacity in the range pH of 7–9 and 1 g/L is the most suitable dosage of AC, considering of the removal rate and adsorption capacity. The adsorption kinetic data and adsorption isotherm data are well described by the pseudo-second order model and Freundlich isotherm model. The maximum equilibrium adsorption capacity is 109.58 mg/g (1 g/L, pH 8.0, 298K). In summary, it is an effective method to prepare AC from sludge and a small amount of peanut shell by using ferric chloride as activator and to remove phenol. This provides a potential option for sludge resource recovery. [ABSTRACT FROM AUTHOR]

This paper studied the removal of diclofenac in FeCeOx catalyzed ultrasonic system. The effects of initial pH, temperature, ultrasonic density and FeCeOx dosage were investigated. Under optimum conditions (pH of 6, temperature of 298 K, ultrasonic density of 2.4 W/cm³, and FeCeOx dosage of 0.7 g/L), more than 80% removal of diclofenac was achieved within 10 min. The kinetic of FeCeOx catalyzed ultrasonic process fitted Behnajady model very well and the reaction rate constant achieved 0.595 min-1. The dechlorination efficiency was more than 70% and the kinetic of dechlorination followed pseudo-second order model. The reaction mechanism was proposed based on the existence of surface cerium and iron and the abundant oxygen vacancies in the FeCeOx catalyst. Ce(III) and Fe(III) could accept the electrons transferred by oxygen vacancy and the generated ¹O2 could attack diclofenac molecules, resulting in their mineralization to inorganic products. [ABSTRACT FROM AUTHOR]

The low-solid sludge concentration in reactors limited application of anaerobic digestion. Forward osmosis technology could be innovatively used for adjusting total moisture content of anaerobic digestion (AD) process in order to achieve a higher solid concentration and smaller reactor volume of AD reactor, for which membrane fouling is a crucial problem and determines the water flux and system performance. Many factors such as flux and composition of feed solution might have influence on the membrane fouling. In high-solid anaerobic digester, total solid could be critical to membrane fouling. A simulative anaerobic digestion forward osmosis membrane bioreactor (adFO-MBR) system was designed for fouling investigation of thin-film composite (TFC) forward osmosis membrane. Anaerobic digestion sludge samples with different total solid (TS) content or with different particle size was used as feed solution in this study. Water flux, adsorption capacity of protein and polysaccharose, SEM-EDX and AIR-FTIR were used for characterization of the pristine and fouled membranes. Experimental results showed that feed solution with TS at 5.5–8.0% had the highest and relatively stable water flux (5.5–7.3 L/m² /h) because of the skeleton support and water passage in sludge with high TS. Water flux with smaller particulates and narrow particle size distribution had a slow decline trend. Adsorption capacity of protein and polysaccharose were positively related with total solid content of AD sludge. The results of this study can suggest us the appropriate parameters of AD sludge in adFO-MBR in terms of membrane fouling control. [ABSTRACT FROM AUTHOR]

In order to improve the efficiency of anaerobic sludge digestion, alkaline and high pressure homogenization (HPH) were combined to pre-treat the excess activated sludge. The effect of HPH operating parameters, including homogenization pressure and cycle number, on the performances of anaerobic sludge digestion was studied. The results demonstrated that the performances of sludge disintegration and anaerobic digestion were markedly enhanced by increasing the homogenization pressure. After pretreatment at a homogenization pressure of 60 MPa with one homogenization cycle combined with an alkaline dosage of 0.04 mol/L, the sludge TCOD, VS removal and cumulative biogas production in a mesophilic anaerobic digestion system increased by 24.68%, 18.95% and 95.81%, respectively, in comparison with that with the alkaline pretreatment alone. But the sludge disintegration and biogas production only slightly increased with the increase of homogenization cycle. Considering biogas production and energy-saving, the suitable homogenization operation was selected as homogenization pressure of 60 MPa with once cycle. Relationships between methane yield and sludge disintegration showed that the improved methane production was mainly attributed to the sludge disintegration resulted from combined sludge pretreatment. [ABSTRACT FROM AUTHOR]

A novel joint method of bioleaching with Fenton oxidation was applied to condition sewage sludge. The specific resistance to filtration (SRF) and moisture of sludge cake (MSC) were adopted to evaluate the improvement of sludge dewaterability. After 2-day bioleaching, the sludge pH dropped to about 2.5 which satisfied the acidic condition for Fenton oxidation. Meanwhile, the SRF declined from 6.45 × 1010 to 2.07 × 1010 s²/g, and MSC decreased from 91.42% to 87.66%. The bioleached sludge was further conditioned with Fenton oxidation. From an economical point of view, the optimal dosages of H2O2 and Fe2+ were 0.12 and 0.036 mol/L, respectively, and the optimal reaction time was 60 min. Under optimal conditions, SRF, volatile solids reduction, and MSC were 3.43 × 108 s²/g, 36.93%, and 79.58%, respectively. The stability and settleability of sewage sludge were both improved significantly. Besides, the results indicated that bioleaching-Fenton oxidation was more efficient in dewatering the sewage sludge than traditional Fenton oxidation. The sludge conditioning mechanisms by bioleaching-Fenton oxidation might mainly include the flocculation effects and the releases of extracellular polymeric substances-bound water and intercellular water. [ABSTRACT FROM AUTHOR]

To improve anaerobic digestion efficiency, combination pretreatment of alkaline and high pressure homogenization was applied to pretreat sewage sludge. Effect of alkaline dosage on anaerobic sludge digestion was investigated in detail. SCOD of sludge supernatant significantly increased with the alkaline dosage increase after the combined pretreatment because of sludge disintegration. Organics were significantly degraded after the anaerobic digestion, and the maximal SCOD, TCOD and VS removal was 73.5%, 61.3% and 43.5%, respectively. Cumulative biogas production, methane content in biogas and biogas production rate obviously increased with the alkaline dosage increase. Considering both the biogas production and alkaline dosage, the optimal alkaline dosage was selected as 0.04 mol/L. Relationships between biogas production and sludge disintegration showed that the accumulative biogas was mainly enhanced by the sludge disintegration. The methane yield linearly increased with the DD COD increase as Methane yield (ml/gVS) = 4.66 DD COD - 9.69. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

To improve the biogas production from corn stovers, a new bionic reactor was designed and constructed. The bionic reactor simulated the rumen digestion of ruminants. The liquid was separated from corn stovers and refluxed into corn stovers again, which simulated the undigested particles separated from completely digested materials and fed back again for further degradation in ruminant stomach. Results showed that the bionic reactor was effective for anaerobic digestion of corn stovers. The liquid amount and its reflux showed an obvious positive correlation with biogas production. The highest biogas production rate was 21.6 ml/gVS-added d, and the total cumulative biogas production was 256.5 ml/gVS-added. The methane content in biogas ranged from 52.2% to 63.3%. The degradation of corn stovers were greatly enhanced through simulating the animal digestion mechanisms in this bionic reactor. [ABSTRACT FROM AUTHOR]