Performance and mechanisms of wastewater sludge conditioning with slag-based hydrotalcite-like minerals (Ca/Mg/Al-LDH)

Weijun Zhang; Haowan Cheng; Sainan Peng; Dandan Li; Hongyu Gao; Dongsheng Wang

doi:10.1016/j.watres.2019.115265

Performance and mechanisms of wastewater sludge conditioning with slag-based hydrotalcite-like minerals (Ca/Mg/Al-LDH)

Water Res. 2020 Feb 1:169:115265. doi: 10.1016/j.watres.2019.115265. Epub 2019 Nov 2.

Authors

Weijun Zhang¹, Haowan Cheng², Sainan Peng², Dandan Li³, Hongyu Gao⁴, Dongsheng Wang⁵

Affiliations

¹ School of Environmental Studies, China University of Geosciences, Wuhan, 430074, Hubei, China; Hubei Provincial Engineering Research Center of Systematic Water Pollution Control, Wuhan, 430074, Hubei, China. Electronic address: zhwj_1986@126.com.
² School of Environmental Studies, China University of Geosciences, Wuhan, 430074, Hubei, China.
³ State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China.
⁴ State Environmental Protection Key Laboratory of Efficient Utilization Technology of Coal Waste Resources, Institute of Resources and Environmental Engineering, Shanxi University, Taiyuan, 030006, PR China.
⁵ Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan, 430074, Hubei, China; State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China.

PMID: 31710914
DOI: 10.1016/j.watres.2019.115265

Abstract

Extracellular polymeric substances (EPS) in wastewater sludge form a network structure that is highly hydrophilic and compressible. Thus chemical conditioning is always required to improve sludge dewaterability by changing the gelatinous structure of sludge flocs. Layered double hydroxides (LDH) are generally characterized by large surface area and high anion exchange capacity, so we prepared three types of hydrotalcite-like compounds (Ca/Mg/Al-LDHs) from a typical solid waste, blast furnace slag, using NaOH precipitation (giving LDH_a), a hydrothermal method (LDH_b), and NaOH-Na₂CO₃ precipitation (LDH_c). The physicochemical properties of the three LDH were comprehensively characterized, and their effectiveness as sludge conditioners was evaluated. The results showed that LDH conditioning was able to promote sludge dewaterability, and conditioning efficiency was strongly dependent on LDH structural properties. LDH neutralized the negative charges onto sludge particles and interacted with EPS to increase floc strength. LDH also formed a skeletal structure that reduced sludge compressibility. In addition, there were interactions between the LDH surfaces and the OC-OH in EPS proteins, which altered the secondary structure of protein molecules, consequently increasing sludge dewaterability. The biomolecules of low-molecular-weight fractions (such as peptides and humic acids) in soluble EPS intercalated LDH. Both the surface complexation of organic matter containing carboxyl groups and the intercalation of small molecules in soluble EPS were responsible for EPS-LDH interactions. The combination of skeleton formation, electrostatic interaction, and EPS-LDH interactions resulted in compression of gel-like structure and improved sludge dewatering performance. We finally suggested a novel sludge treatment process that increases sludge dewaterability using slag-derived Ca/Mg/Al-LDH to condition the sludge, and it could be combined with pyrolysis to prepare multi-functional materials or bio-oil.

Keywords: Adsorption; Chemical conditioning; Coagulation; Extracellular polymers; Layered double hydroxides; Waste activated sludge.

MeSH terms

Aluminum Hydroxide
Filtration
Magnesium Hydroxide
Minerals
Sewage*
Waste Disposal, Fluid
Wastewater*
Water

Substances

Minerals
Sewage
Waste Water
Water
hydrotalcite
Aluminum Hydroxide
Magnesium Hydroxide