A Comparison of Heterogeneous/Homogeneous Crystallization for Phosphate Recovery from Biosolids.

In this study, a fluidized bed reactor was used to compare heterogeneous and homogeneous crystallization for recovering magnesium ammonia phosphate (MAP) from the dewatering filtrate at a municipal water resource recovery facility. Investigating the factors affecting crystallization revealed that pH exerted a greater effect than the Mg/P molar ratio. The results of a heterogeneous crystallization experiment showed that removal efficiency of phosphate (RP%) and crystal efficiency of phosphate (CP%) were 68% and 66%, respectively, at a PO4-P concentration of 200 mg/L, pH of 8.0, and Mg/P molar ratio of 1.0 for 3 h. The reaction rate of heterogeneous crystallization was markedly higher than that of homogeneous crystallization. Those pellets produced through the heterogeneous crystallization exhibited a dense surface (particle size 0.5-1.0 mm; water content 8.7%). Through scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and X-ray diffraction (XRD) examination, the crystallized patterns of the needle-shaped pellets were identified as MgNH4PO4·6H2O.

The characteristics of stepwise ultrasonic hydrolysates of sludge for enhancing denitrification.

The disposal of waste activated sludge (WAS) accounts for approximately 60 % of wastewater treatment plant operating costs. In this study, according to the reaction time and water quality parameters, ultrasonic hydrolysis of WAS is divided into three stages, including floc-disintegration (0-25.2 kJ/g TS), cell-disruption (25.2-36 kJ/g TS), and cell-degradation (over 36 kJ/g TS). The results show that more than 70 % carbon distributes inside the cell, which also contains 63.8 % protein enhancing denitrification capacity. Moreover, cell-degradation hydrolysate has a higher proportion of readily biodegradable COD, indicating that intracellular organic matter is more capable of denitrification than extracellular. Therefore, the optimal ultrasonic operating range is Es = 36-72 kJ/g TS as carbon source, and obtain the hydrolysate with high ratio of soluble chemical oxygen demand to total nitrogen for denitrification. Furthermore, this study supports the comprehensive interpretation of ultrasonic hydrolyzed WAS and the characteristics of hydrolysate as carbon source for enhancing denitrification.

Dynamic fouling behaviors of submerged nonwoven bioreactor for filtration of activated sludge with different SRT.

The flux variations and resistances accumulated during filtration of activated sludge with sludge retention time (SRT) of 15, 30, and 60 days were analyzed to investigate the dynamic fouling behavior in a submerged nonwoven bioreactor. Different SRT values varied sludge condition and particle size distribution in the supernatants, which caused dissimilar fouling characteristics. Short-term fouling of the nonwoven bioreactor during filtration of activated sludge with SRT of 15 days was fully reversible, and the resistance percentages of solutes, colloids, and suspended solids were 6%, 27%, and 67%, respectively. On the other hand, significant increases of colloid resistance, such as with the filtration of activated sludge with SRT of 30 and 60 days, were related to the occurrence of irreversible fouling. The phenomenon of pore blocking by particles or colloids with size analogous to the pore of nonwoven fabric was a decisive factor leading to irreversible fouling in the large-pore materials.

Comparison of polyhydroxyalkanoates production by activated sludges from anaerobic and oxic zones of an enhanced biological phosphorus removal system: effect of sludge retention time.

This study compared the PHAs production behavior of sludges from the anaerobic and oxic phases of an enhanced biological phosphorus removal (EBPR) system. This was accomplished by using the kinetics and stoichiometric coefficients obtained from aerobic batch tests to evaluate the performance of these two sludges. Experimental results indicated that the metabolic behavior of the sludges for PHAs production depend significantly on the operating sludge retention time (SRT) of the EBPR system. The oxic sludge with 5 days of SRT exhibited better PHAs production performance than anaerobic sludge. Conversely, the anaerobic sludge with 15 days of SRT had superior PHAs production capability compared to oxic sludge. These comparisons suggest that whether anaerobic or oxic sludge should be employed for PHAs production depends mainly on the operating SRT of the EBPR system.

Effects of different carbon supplements on phosphorus removal in low C/P ratio industrial wastewater.

This study focuses on the effects of different carbon supplements on biological phosphorus removal in the optonics and semiconductor industrial wastewater treatment. Experimental results demonstrate that the addition of a carbon source (glucose, acetate, and digester supernatant) improved phosphorus removal effectively. When the COD/P ratios were controlled in the range of 18-20 (using glucose and supernatant as supplement), the acclimated sludge showed more than 98% removal of phosphorus. In addition, different organic carbons induce dissimilar behavior in anaerobic release and aerobic uptake of phosphorus. The glucose supplement induces significant phosphorus release in anaerobic phase and then an increased phosphorus uptake in aerobic phase. The released phosphorus descended in anaerobic phase when acetate and supernatant were added. There was a good linear relationship of first order reaction between initial COD concentration and specific substrate utilization rate in anaerobic phase.

The effects of soluble organic matters on membrane fouling index.

This study investigated the effects of soluble organic matters on membrane fouling characteristics, using silt density index (SDI) and modified fouling index (MFI) to evaluate the fouling potential. Experimental results demonstrated that humic acid had significant effects on membrane fouling indexes. When its concentration was in the range of 0.01-0.05 mg/L, the SDI(15) and MFI were 2.9-3.9 and 5.4-13.8s/L(2), respectively. According to the linear equations of MFI measurements, the fouling potential was in the order of humic acid>nucleic acid protein>glucose. Moreover, the molecular weight of dextran played an important role in membrane fouling indexes. Furthermore, a mathematical analysis of filtration experiments based on saturation curve was developed in this study. The maximum accumulated filtrate (V(max)) and the constant of filtration (k(f)) could be obtained to improve the precision of membrane fouling prediction.

Comparative study on the degradation of I.C. Remazol Brilliant Blue R and I.C. Acid Black 1 by Fenton oxidation and Fe 0/air process and toxicity evaluation.

Degradation of Remazol Brilliant Blue R (anthraquinone dye) and Acid Black 1 (azo dye) by Fenton oxidation and low-cost Fe(0)/air process was compared. The doses of Fenton reagent needed for decolorization of Remazol Brilliant Blue R was much higher than for Acid Black 1. The Fe(0)/air process rapidly decolorized dyes within 5 min at the Fe(0) doses of 10 and 50 g L(-1) for Remazol Brilliant Blue R and Acid Black 1, respectively. COD removals of Remazol Brilliant Blue R and Acid Black 1 by the Fe(0)/air treatment were significantly higher than those by Fenton oxidation. 98% COD of Remazol Brilliant Blue R was removed by the Fe(0)/air process. The toxicity of Fe(0)/air-treated solution was significantly lower than that of Fenton-treated solution; no toxicity was detected after the treatment of Remazol Brilliant Blue R by the Fe(0)/air process. Fe(0)/air technique is a potential process for dye degradation.