[Preparation and Comparison of Arsenic Removal Granular Adsorbent Based on Iron-Manganese Sludge].

Backwashing sludge is an efficient adsorbent for arsenic removal. However, considering the practical application, it is unfavorable for solid-liquid separation. To overcome this disadvantage, a high-temperature baking method was used to prepare a granular adsorbent (GA) with iron-manganese sludge, along with an embedding method with drying (H-GA) and lyophilization (D-GA). The characterization results showed that the surface of the three adsorbents were rough, with specific surface areas of 43.830, 110.30, and 129.18 m2·g-1, respectively. The adsorption experiments showed that the adsorption of arsenic by H-GA and D-GA was much higher than that of GA. The maximum adsorption capacities of GA, H-GA, and D-GA were 5.05, 14.95, and 13.45 mg·g-1, respectively. The Langmuir model fit the adsorption process of arsenic by H-GA and D-GA better, whereas the Freundlich model fit the adsorption process of GA better. The Pseudo-first order model and Pseudo-second order model were suitable to describe the kinetic curves of the three adsorbents. The acidic environment was more conducive to the adsorption of arsenic. The particle adsorbents prepared by the embedding method, H-GA and D-GA, retained the original structure of iron-manganese sludge, and the specific surface area was much larger than that of GA; thus, the adsorption capacity was greater than that of GA. Drying and lyophilization had no significant effect on the adsorption performance of granular adsorbents prepared by embedding.

[Start-up and Operation of Biofilter Coupled Nitrification and CANON for the Removal of Iron, Manganese and Ammonia Nitrogen].

A pilot-scale bio-filter coupled nitrification and CANON was started up to remove iron, manganese and ammonia nitrogen from groundwater in a plant, and the main removal route of ammonia nitrogen was analyzed. The experiment showed that the bio-filter could be started up successfully and achieved stable operation after 164 days of culture development. The value of △NH4+-N/△NO3--N was 1.49, and the oxidation and removal of Fe(Ⅱ), Mn(Ⅱ), and NH4+-N were (9.87±1.17), (2.25±0.06), and (1.51±0.06) mg·L-1, respectively. The calculation based on the quantitative relationship between nitrogen conservation and dissolved oxygen (DO) measurement indicated that the contribution of CANON to NH4+-N removal was 33.48%-38.87%, and the average ratio of ammonia nitrogen removal amount to DO was 1:3.79-1:3.94. The removal ratio of ammonia nitrogen was lower with lower temperature.

[Effect of Intermediate-Setting Aeration on the CANON Granular Sludge Process in the AUSB Reactor].

The impact of different aeration positions on startup and operation of the continuous flow CANON granular sludge process was considered by inoculating flocculent ANAMMOX activated sludge at room temperature (25±1)℃ in two sets of AUSB reactors. The aeration unit of R1 was installed 0.3 m above the base, while the aeration unit of R2 was set at the bottom. R1 and R2 successfully developed the granule CANON process on the 43rd d and 56th d, respectively. The mean particle diameter of R1 granular sludge increased to 214.79 µm, and the eigenvalue (△NO3--N/△TN) was maintained at 0.128; whereas, the granular sludge size of R2 rose to 205.27 µm with an eigenvalue maintained at 0.129. The nitrogen loading rate (NLR) was gradually increased in the low ammonia-nitrogen (90 mg·L-1) wastewater within R1 and R2. This was more beneficial in R1, resulting in the persistent growth of CANON granular sludge and the enhancement of the systematic nitrogen removal rate (NRR). The average particle diameter of R1 rose to 507.46 µm in 88 d, while NRR reached up to 0.277 kg·(m3·d)-1. R2 granule sludge particle size was 467.72 µm after 108 d of cultivation, and achieved a 0.243 kg·(m3·d)-1NRR, which was 87.73% of that in R1. During the course of steady operation, the specific anoxic/aerobic mode of R1 effectively suppressed NOB microbial activity, the eigenvalue remained around 0.127±0.003, and the NRR of R1 was maintained at about (0.262±0.019) kg·(m3·d)-1. However, NOB was propagated observably in the continuously aerobic R2, whose eigenvalue rose to 0.136±0.004, while NRR was merely (0.231±0.015) kg·(m3·d)-1 after 125 d of long-term operation. During the whole experiment period, the intermediate-setting aerated AUSB accelerated the formation of CANON granular sludge evolving from flocculent ANAMMOX sludge, and better nitrogen removal performance and operational stability were achieved.

[Arsenic(â ¤) Removal by Granular Adsorbents Made from Backwashing Residuals from Biofilters for Iron and Manganese Removal].

Granular adsorbents for arsenic removal (GA) made from the backwashing residuals from iron and manganese removal biofilters for groundwater were characterized and examined as an arsenate sorbent. The GA were characterized by SEM-EDS microscopy, X-ray diffraction (XRD), and BET surface area measurement. The results showed that the GA had rough surfaces, developed pores, and were mainly amorphous, with small fractions of crystalline quartz and hematite. The surface area of the GA, which consists of many mesopores, was 43.8 m2·g-1. The kinetic studies revealed that arsenate adsorption on the GA was described by a pseudo-second-order kinetic equation, and the Freundlich isotherm equation fit the arsenate adsorption well (R2=0.994). The maximum adsorption capacity calculated by the Langmuir isotherm equation for As(Ⅴ) was 5.05 mg·g-1. Further studies showed that the GA operated well for As(Ⅴ) removal over a broad range in pH from 1.1 to 9.5. The coexistence of HCO3- and SO42- had no great influence on arsenic adsorption, while the H2PO4- and SiO32- showed negative effects. The GA can be regenerated well, and 82% of the original adsorption capacity was maintained after three regeneration cycles.