Effect of Organic Substances on Nutrients Recovery by Struvite Electrochemical Precipitation from Synthetic Anaerobically Treated Swine Wastewater.

Anaerobically treated swine wastewater contains large amounts of orthophosphate phosphorus, ammonium nitrogen and organic substances with potential nutrients recovery via struvite electrochemical precipitation post-treatment. Lab-scale batch experiments were systematically conducted in this study to investigate the effects of initial pH, current density, organic substances upon nutrients removal, and precipitates quality (characterized by X-ray diffraction, scanning electron microscopy and element analysis via acid dissolution method) during the struvite electrochemical precipitation process. The optimal conditions for the initial pH of 7.0 and current density of 4 mA/cm2 favoured nutrients removal and precipitates quality (struvite purity of up to 94.2%) in the absence of organic substances. By contrast, a more adverse effect on nutrients removal, morphology and purity of precipitates was found by humic acid than by sodium alginate and bovine albumin in the individual presence of organic substances. Low concentration combination of bovine albumin, sodium alginate, and humic acid showed antagonistic inhibition effects, whereas a high concentration combination showed the accelerating inhibition effects. Initial pH adjustment from 7 to 8 could effectively mitigate the adverse effects on struvite electrochemical precipitation under high concentration combined with organic substances (500 mg/L bovine albumin, 500 mg/L sodium alginate, and 1500 mg/L humic acid); this may help improve struvite electrochemical precipitation technology in practical application for nutrients recovery from anaerobically treated swine wastewater.

[Difference of P content in different area substrate of constructed wetland].

Adsorption of substrate is the main removal mechanisms of phosphorus in constructed wetland. It is easily impacted by various environmental factors existing in the wetland bed. The contents of substrate TP and the main inorganic P in different areas of both horizontal sub-surface flow constructed wetland with plant and one without plant were measured after treating wastewater five months. Different areas of the wetland with plant differed greatly in the substrate TP. Rhizosphere substrate in front area had the highest TP content and achieved 0.75 g x kg(-1), and the TP content of non-rhizosphere substrate in back area was only 0.21 g x kg(-1). The TP content of substrate in different areas of the wetland without plant had a little variety and ranged only between 0.21 and 0.27 g x kg(-1). Averagely, the substrate TP content in the wetland with plant was higher than the one in the wetland without plant. The phosphorous with Fe-bound (Fe-P), Al-bound (Al-P), and Ca-bound (Ca-P) were main inorganic phosphorous existing in the substrate in both wetlands, their contents in different areas substrate all increased, compared with the one before experiment. Fe-P and Al-P in different substrates in both wetlands had a similar variety. Their content between rhizosphere and intermediate substrate of front area in the wetland with plant and other area substrate in both wetlands differed greatly because the former increased greatly. Compared with Fe-P and Al-P, the variety of Ca-P in different substrates in both wetlands was low. But the content of Ca-P in rhizosphere substrate in wetland with plant was higher than other two parts respectively in front and back areas. Obviously, the plant root had an impact on the phosphorous content of substrate in constructed wetland. For TP, Fe-P, Al-P, Ca-P and loosely sorbed phosphorous in substrate, it increased with distance of the root.

[Characterization of Cr (VI) removal and total Cr equilibrium adsorption by sulfate reducing granular sludge in stimulant wastewater].

Sulfate reducing granular sludge (SRGS) cultivated in small scale EGSB reactor was used for Cr (VI) removing. Characterization of Cr (VI) removal and total Cr equilibrium adsorption was studied, and the adsorption isotherm was fitted. Results showed that removal of Cr (VI) was in connection with the structure and chemical composition of SRGS and several environmental factors. The Cr (VI) removal rate increased with the dosage of granular sludge; the increasing of oscillation speed and temperature could enhance Cr (VI) removal and total Cr adsorption, but while the oscillation speed reached 150 r x min(-1) or the temperature came to 40 degrees C, the physical structure of granular sludge would be affected and the granular sludge discrete, and total Cr equilibrium adsorption decreased; lower pH value caused higher Cr (VI) removal rate, however the sulfate on the surface of granular sludge was affected by lower pH value easily and would translate into H2S, then total Cr adsorption rate decreased. Cr (VI) removal would be influenced by physical, chemical and biological factors, and the process included reduction and adsorption mainly. The maximum adsorption of total Cr by granular sludge was 6.84 mg x g(-1), and the total Cr adsorbing process fitted in with Langmuir adsorption isotherm.