Settleability and dewaterability of sewage sludge with modified diatomite

Experimental investigation on sludge conditioning and dewatering using an agricultural biomass coupled with resource recovery

In this study, the effect of modified areca husk fibre biochar (MAFB-AlCl3) on dairy sludge conditioning and dewatering along with raw and modified coconut shell biochar (MCSB-FeCl3) was investigated. Further, MgO impregnated biochars of areca husk fibre and coconut shells was carried out to evaluate the performance on phosphate recovery from the diary sludge. The enhancement in sludge dewatering with MAFB-AlCl3 were evaluated experimentally and significant reduction of capillary suction time (CST) (51.6 %), moisture content (18%), zeta potential (1.3 mV) and increased settleability (32.7%) were observed. The sludge conditioning parameters namely dosage (% of dry solids (DS)), rapid mixing time (RMT), slow mixing time (SMT) were optimized by response surface methodology for the modified biochars. Optimum CST (31.51 s) was obtained at dosage (50 % of DS), RMT (9.89 min) and SMT (17.23 min). Results of batch study for phosphate recovery by MgO impregnated biochars (MgB) was found to be 96.6 % and 100 % by MgB of areca husk fibre (MgAFB) and coconut shells (MgCSB) respectively. The morphological characteristics and elemental distribution using field emission scanning electron microscopy (FE-SEM) & energy dispersive X-ray spectroscopy (EDS) reveals the structural change in the sludge particles for the modified biochars as well as for sludge. Hence MAFB-AlCl3, MgAFB and MgCSB is proved to be suitable and an effective candidate for sludge conditioning and dewatering coupled with phosphate recovery in handling the diary sludge.

Application of coffee ground-based skeleton builder with FeCl3 for conditions of pre-dewatered sludge toward further deep dewatering

Skeleton builders are essential for achieving deep sludge dewatering. In this study, a novel spent coffee ground (SCG)-based skeleton builder was developed to attain deep sludge dewatering by combined conditioning with FeCl3, and possible mechanisms were examined. Through different surface analysis techniques, it was demonstrated that at a pyrolysis temperature of 300 °C, the spent coffee ground biochar (SCGB-300) has an intact pore structure, a rigid carbon skeleton, and large oxygen-containing functional groups, making it the best skeleton builder for sludge dewatering. When combined with FeCl3 for conditioning, the structure of SCGB-300 remained intact under high pressure and played important role. The rich porous structure facilitated water drainage. During the sludge conditioning, small amount of positive charge on the surface of SCGB-300 further increased the zeta potential of sludge through charge neutralization. At the same time, the adsorption of SCGB-300 removed viscous hydrophilic substances and further improved the dewatering performance. At an optimum dosage of 6% (dry solid, DS) FeCl3 and 30% SCGB-300 (DS), the moisture content of sludge was reduced from 85.47% to 63.35%, and the dewatering rate was increased from 46.08% to 70.03%. Therefore, SCGB is a promising skeleton builder for sludge conditioning and deep dewatering.

Effect of chemical regulation combined with mechanical filtration on deep dewatering and consolidation characteristics of sludge

To reveal the mechanism underlying deep dewatering of municipal sludge, this paper investigated the sludge characteristics from the perspective of soil mechanics, and analyzed the sludge physical and mechanical properties, stress as well as dewatering behavior during the dewatering process. Before and after cationic polyacrylamide (CPAM) and chitosan (HACC) conditioning, the pressure filtration dewatering time of treated sludge was shorter than that of raw sludge, and the water removal rate was greater than 70% at the 6 MPa pressure. However, with the increase in filter pressing time, the filtration resistance coefficient of sludge increased, and the water pressure in sludge pores rose up, and a longer time was needed for dissipation at the larger pressure, resulting in the slowdown of sludge consolidation. In addition, based on the three-stage Terzaghi Voigt model, when the pressure rose from 2 to 6 MPa, the time from filtration stage to compression stage of raw sludge was shortened, and the second stage played the most important role in the dewatering process. Compared with the raw sludge, the sludge filtration stage was shortened after CPAM or HACC conditioning, and the main dewatering mechanism changed from the second compression stage to the first compression stage, which means the bound water in sludge flocs was transformed into free water. This was also the reason why the dewatering, compression and consolidation rate of the conditioned sludge was faster than that of the raw sludge.