[Properties of Biochars Prepared from Different Crop Straws and Leaching Behavior of Heavy Metals].

In this study, rice straw, soybean straw, wheat straw, and corn straw were chosen as raw materials, and biochars were prepared through the pyrolysis method at 550℃ under oxygen-limited conditions to investigate the physicochemical properties of biochars derived from the straws, the migration and transformation characteristics of heavy metals (HMs) (Cr, Ni, Cu, As, Cd, and Pb) after pyrolysis, and their leaching behaviors in different leaching solutions. The results showed that the physicochemical properties and elemental composition of the biochars were basically consistent. However, compared with that of biochars derived from other straws, biochar derived from wheat straw had a higher ash content (22.48%) and H/C radio (0.06). Meanwhile, biochar derived from corn straw had a smaller micropore volume (0.006 cm3·g-1) and a correspondingly smaller specific surface area (110.120 m2·g-1), which was consistent with the SEM image. After pyrolysis, the content of HMs (except Cd) increased by 14.04% to 410.81%, especially that of Cu and As. However, the content of Cd in soybean straw and corn straw decreased by 20.49% and 8.20% after pyrolysis, respectively, due to the low boiling point of Cd. Furthermore, most of the HMs (except Cd and Pb) tended to transform from unstable (acid-soluble/exchangeable and reducible forms) to stable forms (oxidizable and residual forms), implying that pyrolysis facilitated the stabilization of the HMs. The HMs in biochar were not leached or were leached in small amounts in ultra-pure water and buffered salt solutions, as opposed to leaching in relatively larger amounts in acetic acid solution and humic acid solution. Cr and Ni showed low leaching capacity in all leaching solutions. Cu showed relatively high leaching capacity in acetic acid solution, with the leaching amount ranging from 2.601 mg·kg-1 to 4.224 mg·kg-1, and As showed a relatively high leaching capacity in humic acid solution, with the leaching amount ranging from 0.074 mg·kg-1to 0.166 mg·kg-1. After pyrolysis, the environmental quality index (PIi) and the Nemerow pollution index (NPI) values of various HMs increased by different degrees. However, the pollution of single HMs remained at a safe level, and the integrated pollution of biochars was at the level of "clean". Due to the significant increase in potential ecological risk factors (Er) of Ni, Cd, and Pb after pyrolysis, the potential ecological risk index (RI) of biochar derived from the rice straw increased slightly. However, the potential ecological risk indexes of biochars derived from other straws significantly decreased after pyrolysis, owing to the stabilization of HMs.

Particular internal recirculation frequency scope for enhancing denitrifying phosphorus removal in an oxidation ditch.

This study investigated the influence of the unique internal recirculation characteristics of an oxidation ditch (OD) system, namely, the internal recirculation frequency (IRF) on denitrifying phosphorus removal (DNPR). The ratios of denitrifying polyphosphate-accumulating organisms (DPAOs) to polyphosphate-accumulating organisms (PAOs) under different IRF conditions were measured using a batch experiment. On this basis, the variation of nutrient transformations was studied using the IRF changes by the mass balance method. The results showed that, for the OD system that had an anaerobic zone upstream from the circular corridor and set anoxic and aerobic zones along the circular corridor, when the IRF was between 3.4 h-1 and 7.5 h-1, the DPAOs/PAOs ratio reached about 50%. Approximately 20% of the total phosphorus (TP) was removed and over 11% of the total nitrogen (TN) was transformed into nitrogen gas by the DNPR process, and meanwhile the total removal efficiencies of the TP and TN were over 93% and 80%. When the IRF was greater than 11.5 h-1, the TN removal efficiency decreased significantly, and this was not conducive to simultaneous nitrogen and phosphorus removal. The results indicated that the OD process would possess a better DNPR potential if the IRF were controlled within the proper scope.

[Effects of Long-term Poly-P Deficiency on the Metabolic Properties of Accumulibacter in AO-SBR System].

To investigate the changes in microbial community structure and metabolic properties of Accumulibacter under long-term Poly-P deficiency, an activated sludge enriched with Accumulibacter was inoculated into two SBR reactors, where sodium acetate and sodium propionate were used separately as organic carbon sources. The two reactors were operated for 60 days with an influent PO43--P concentration of 2.5 mg·L-1. The phosphorus removal performance, sludge production, and changes in the microbial community structure of the systems were analyzed. The results indicated that both SBR systems showed good performance of phosphorus and organic matter removal. However, microorganisms in both systems showed glycogen-accumulating metabolism properties under long-term Poly-P deficiency. In the unfavorable environment of long-term Poly-P deficiency, Accumulibacter Ⅰ maintained a high abundance (40%±7%) in the propionate SBR system, indicating that Accumulibacter Ⅰ had higher metabolic activity and its metabolic properties could be independent of Poly-P for survival under Poly-P deficiency for a long period. In comparison, propionate is more conducive to Accumulibacter adaptation to lower phosphorus loads, and Accumulibacter Ⅰ is more competitive than Accumulibacter Ⅱ under lower phosphorus loads.

Determination of textile dyeing wastewater COD components by comparison with respirometry and full-scale data.

A Modified Activated Sludge Model No. 1 (M-ASM1), including six COD components (S1, S(S), X1, X(S), X(H), and S(O)) and three biochemical processes (aerobic growth of heterotrophs, aerobic decay of heterotrophs and hydrolysis of entrapped organics) was used to simulate the anaerobic hydrolysis-aeration-sedimentation treatment series in a full-scale textile dyeing wastewater treatment plant (WWTP) with an influent flow rate of 200,000 m3/d. Using a respirometry method, the influent COD components of the WWTP activated sludge system were estimated. Then, calibration equations were set up depending on the full-scale treatment plant running data in order to calibrate the measurement results. This paper indicates that the influent COD components of a low biodegradability wastewater can be estimated using a respirometry method coupled with a calibration procedure based on full-scale plant running data.

Effect of denitrification type on pH profiles in the sequencing batch reactor process.

Laboratory batch experiments were conducted to investigate pH profiles during partial and complete denitrification with sufficient organic carbon source. Five stirred tank-type glass vessels, with a 7 L working volume for each, were used as SBR reactors that were all operated in denitrification mode. Five levels of initial proportion of nitrogen substances, i.e. nitrate and nitrite, were used in five reactors, respectively. Results showed that, at given temperature and mixed liquor suspended solids (MLSS), partial denitrification could attain a higher pH value than complete denitrification at the end of denitrification with the same initial NOx- concentration. The larger proportion the nitrite took in initial NOx- concentration, the higher pH peak would be obtained on pH profiles during denitrification despite the same total alkalinity produced. It was found that different types of alkalinity were produced during biological denitrification with different nitrogen substances. Partial denitrification could more carbonate alkalinity produce than complete denitrification. Furthermore, some characteristic points were identified on pH profiles which could indicate the disappearance of not only nitrate, but also nitrite in system. When computers are used to detect these features, they can provide rapid, real-time information, regarding the biological state of the system.

Applying real-time control to enhance the performance of nitrogen removal in CAST system.

A bench-scale reactor(72 L) red with domestic sewage, was operated more than 3 months with three operation modes: traditional mode, modified mode and real-time control mode, so as to evaluate effects of the operation mode on the system performance and to develop a feasible control strategy. Results obtained from fixed-time control study indicate that the variations of the pH and oxidation-reduction potential(ORP) profiles can represent dynamic characteristics of system and the cycle sequences can be controlled and optimized by the control points on the pH and ORP profiles. A control strategy was, therefore, developed and applied to real-time control mode. Compared with traditional mode, the total nitrogen(TN) removal can be increased by approximately 16% in modified mode and a mean TN removal of 92% was achieved in real-time control mode. Moreover, approximately 12.5% aeration energy was saved in real-time control mode. The result of this study shows that the performance of nitrogen removal was enhanced in modified operation mode. Moreover, the real-time control made it possible to optimize process operation and save aeration energy.