Reduced cathodic scale and enhanced electrochemical precipitation of Ca2+ and Mg2+ by a novel fenced cathode structure: Formation of strong alkaline microenvironment and favorable crystallization.

Electrochemical precipitation is a promising technique for hardness abatement without the addition of external ions. However, the scale layer on cathode deteriorated the removal efficiency and limited the practical application. Herein, a fenced cathode structure was designed to prevent cathodic precipitation. The cathode was fenced by a crystallization-inducing material for separating the OH- production and crystallization processes. Precipitation on the cathode was confirmed to shift to the crystallization-inducing material, and the clean fenced cathode provided efficient long-term OH- production. At a current density of 40 A/m2, the Ca2+ or Mg2+ removal efficiency increased by 12.8% or 46.1%, respectively, compared to those of a traditional cathode. Thermodynamic equilibrium in synthetic water and mine water, mass transfer and the location of precipitation were analyzed to elucidate the electrochemical precipitation process. The enhanced mechanism was ascribed to the crystallization-inducing material, which remarkably promoted the crystallization process, and hindered OH- migration, thereby increased the pH of alkaline microenvironment. Notably, a recovery design was proposed to recover pure calcite and brucite from alkalinity-free wastewater. The design reveals a promising strategy for enhancing the crystallization process and reducing cathodic scale, also initiating a new research direction toward hardness removal.

Two-phase high solid anaerobic digestion with dewatered sludge: Improved volatile solid degradation and specific methane generation by temperature and pH regulation.

The effects of temperature and pH on volatile solid (VS) degradation and CH4 production of anaerobic digestion treating high-solid municipal dewatered sludge was studied. There were two single-phase reactors in Group 1: 35 and 55 °C reactors. In Group 2 (G2), acidification phase temperature was 55 °C or 70 °C and digestion phase temperature was 35 °C or 55 °C. G3 was set on the basis of G2 with the initial pH adjusted to 10.0. VS degradation ratio and CH4 generation ratio of G2 and G3 were higher than G1. In G2, acidification reactors did not show much difference on VS degradation and CH4 generation. Higher VS degradation ratio with higher CH4 generation ratio was get in extreme thermophilic/thermophilic-mesophilic systems. In G3, pH adjustment only promoted VS degradation and CH4 generation in acidification reactors when compared to G2, but the two ratios of the whole systems was not further enhanced.

Biodegradation of polyacrylamide by anaerobic digestion under mesophilic condition and its performance in actual dewatered sludge system.

Polyacrylamide (PAM) used in sludge dewatering widely exists in high-solid anaerobic digestion. Degradation of polyacrylamide accompanied with accumulation of its toxic monomer is important to disposition of biogas residues. The potential of anaerobic digestion activity in microbial utilization of PAM was investigated in this study. The results indicated that the utilization rate of PAM (as nitrogen source) was influenced by accumulation of ammonia, while cumulative removal of amide group was accorded with zeroth order reaction in actual dewatered system. The adjoining amide group can combined into ether group after biodegradation. PAM can be broken down in different position of its carbon chain backbone. In actual sludge system, the hydrolytic PAM was liable to combined tyrosine-rich protein to form colloid complex, and then consumed as carbon source to form monomer when easily degradable organics were exhausted. The accumulation of acrylamide was leveled off ultimately, accompanied with the yield of methane.

[Effects of mild thermal pretreatment on anaerobic digestibility of sludge with low organic content].

The effects of mild pretreatment at temperature of 100 degrees C on the solubilization anP anaerobic digestibility of high solid sludge with low organic content were studied with the variation of heating times. Experimental results show soluble organic concentrations in supernatant increase with the prolonging of thermal pretreatment time rapidly, and slowly after 30 min. The dissolution rates of COD, protein and carbohydrate with 30 min of thermal pretreatment at 100 degrees C were 10.5%, 11.6% and 8.2%, respectively. Mild thermal pretreatment not only enhanced total methane yield, but also advanced the peak time of methane production. The methane production ratio with 30 min of thermal hydrolysis was 136 mL.g-1 (VS) at day 10 of anaerobic digestion, with an 86% increase over the control group. VS reduction ratio after 30 days anaerobic digestion o also increased to 33.3% with 30 min of thermal pretreatment at 100 degrees C compared with 19.1% in control group. In addition, studies on enzymatic activity indicated the activities of four key enzymes (protease, acetokinase, phosphotransacetylase and coenzyme F420) involved in anaerobic digestion were all enhanced by mild thermal pretreatment.