Waste waters from the waste paper industry and landfill leachates contain high calcium concentrations. Treatment of those waste waters in an anaerobic system will lead to extensive precipitation of calcium carbonates. Problems due to accumulation of calcium carbonate in anaerobic reactors can be avoided by applying a crystallization reactor to remove calcium from the influent. This solution, however, is expensive due to the need to dose alkalinity. In this paper, the possibility of reusing the produced alkalinity by recirculating anaerobic effluent was investigated. Calculations and experiments were carried out to investigate to what extent calcium could be removed from the influent. Experiments were carried out in a 4.5 1 UASB reactor and a 0.8 1 crystallization reactor, seeded with sand. The influent contained up to 1800 mg.l −1 calcium and the substrate was acetic acid. Removal of calcium from the influent could be successfully accomplished. Recirculation of the anaerobic effluent supplied sufficient bicarbonate alkalinity for crystallization. Consequently, no extra chemicals (i.e. Na 2 CO 3 and/or NaOH) were needed. A chemical equilibrium model, with adapted pseudo solubility products, is a very useful tool to determine the proper recycle ratio of effluent for optimal performance.

E.P.A. van Langerak

H.V.M. Hamelers

G. Lettinga

Water Science & Technology

WATER SCIENCE AND TECHNOLOGY 发表关于水和废水科学技术各个方面的同行评议论文。论文通过严格的同行评审程序选择，旨在快速和广泛地传播研究成果、新技术的开发和应用以及相关的管理和政策问题。科学家、工程师、顾问、管理人员和政策制定者会发现这本期刊作为研究活动及其实际应用进展的永久记录是必不可少的。

The journal "Water Science and Technology" publishes peer-reviewed papers on all aspects of water and wastewater science and technology. Papers are selected through a rigorous peer review process, aimed at the rapid and broad dissemination of research findings, the development and application of new technologies, and related management and policy issues. Scientists, engineers, consultants, managers, and policymakers will find this journal an essential record of the progress of research activities and their practical applications.

《Water Science and Technology》期刊发表关于水和废水科学技术各个方面的同行评审论文。所有论文经过严格的同行评审程序，旨在快速而广泛地传播研究成果、新技术的开发与应用，以及相关的管理和政策问题。科学家、工程师、顾问、管理人员和政策制定者将发现，这本期刊是研究活动及其实际应用进展的重要记录。

Category	Quartile
环境科学与生态学	4
环境科学与生态学, 工程环境	4
环境科学与生态学, 环境科学	4
环境科学与生态学, 水资源	4

Influent calcium removal by crystallization reusing anaerobic effluent alkalinity

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