Capture of perchlorate by a surface-modified bio-sorbent and its bio-regeneration properties: Adsorption, computations and biofouling

Bioregeneration of sulfate-laden anion exchange resin

Ion exchange technology removes ionic compounds from waters effectively but treatment of the spent regenerant is expensive. The bioregeneration of sulfate-laden strong base anion exchange resin was successfully tested using both pure and mixed sulfate-reducing bacterial cultures. The resin was first used for removal of sulfate from neutral (pH 6.7 ± 0.5) synthetic sodium sulfate solutions, after which the spent resin was regenerated by incubating with a viable sulfate-reducing bacterial culture in batch and column modes. In the batch bioregeneration tests, the achieved bioregeneration was 36-95% of the original capacity of the fresh resin (112 mg SO₄^2-/g) and it increased with regeneration time (1-14 days). The capacity achieved in the column tests during 24 hours of bioregeneration was 107 mg SO₄^2-/g after the first regeneration cycle. During the bioregeneration, sulfate was mainly reduced by the sulfate-reducing bacteria (approx. 60%), but part of it was only detached from the resins (approx. 30%). The resin-attached sulfate was most likely replaced with ions present in the liquid sulfate-reducing bacterial culture (e.g., HCO₃^-, HS^-, and Cl^-). During the subsequent exhaustion cycles with the bioregenerated resin, the pH of the treated sodium sulfate solution increased from the original 6.7 ± 0.5 to around 9. The study showed that biological sulfate reduction could be used for sulfate removal in combination with ion exchange, and that the exhausted ion exchange resins could be regenerated using a liquid sulfate-reducing bacterial culture without producing any brine.

Perchlorate occurrence in foodstuffs and water: Analytical methods and techniques for removal from water - A review

Perchlorate (ClO₄^-), a type of contaminant with high diffusivity and durability, has been widely detected in water and foodstuffs, arousing a global concern. It can interfere with normal function of the human thyroid gland, affecting human health. Therefore, determination of perchlorate in water and foodstuffs, and removal from water are important. This review focuses on the occurrence of perchlorate, mainly in water and foodstuffs, and provides an overview of analytical methods for determination of perchlorate over the last two decades. In addition, merits and drawbacks of the various methods have been considered. This review also highlights the most commonly used approaches for removal of perchlorate from water. Finally, current trends and future perspectives in determination of perchlorate and removal from water are proposed. This review provided a comprehensive understanding of perchlorate occurrence and its removal from water, and had practical significance in reducing the harm of perchlorate to human.

Modified biogas residues as an eco-friendly and easily-recoverable biosorbent for nitrate and phosphate removals from surface water

Effective managements of organic solid waste and surface water eutrophication can reuse/reduce solid waste resources, and ensure surface water safety. Herein, an easily-recoverable amine-functionalized biosorbent was developed from biogas residue (BR-N) for nitrate and phosphate removals from surface water. Physicochemical characteristics revealed that BR-N has a cross-staggered structure with abundant quaternary-amine groups to enhance the diffusion and electrostatic attraction of nitrate/phosphate. In batch studies, nitrate/phosphate could be effectively removed by the BR-N within a wide pH range of 5.0-9.0, and the maximum adsorption capacities of BR-N were 64.12 mg/g for nitrate and 34.40 mg P/g for phosphate. After continuous 8 cycles of adsorption-desorption, BR-N still exhibited >82% adsorption capacity for nitrate/phosphate removals, implying the high chemical stability and reusability for water treatment. Whereafter, BR-N has real application prospect in water treatment, which could effectively treat ˜380, ˜260 and ˜760 bed volumes (BV) of three actual eutrophic surface water to satisfy the surface water standard of China (GB3838-2002). The cost of BR-N was 2.89 $/kg evaluated by energy-economy assessment, indicating the low-cost production of biogas residue-based adsorbent for treating eutrophic surface water. Overall, this study provides a new idea for high-value utilization of organic solid waste and purification of eutrophic water.