Biological water treatment processes are based on the growth of microbial communities capable of metabolizing contaminants through mediating oxidation–reduction reactions. Biologically active filters (BAFs) are applied in drinking water treatment for the removal of contaminants including natural organic matter, nitrate, trace organic compounds, perchlorate, sulfate, iron, and manganese. BAFs make use of a fixed film that develops on media such as sand, anthracite, granular activated carbon, or membranes. This biofilm is a diverse community, but the conventional biological treatment process basically takes a “black box” approach with respect to microbial community development. Controlling biofilm thickness and producing microbial communities fully adapted to target contaminants represent significant engineering challenges. This article discusses the advantages and applications of BAFs to remove contaminants in drinking water sources, reviews microbial communities in bulk water and biofilms, and summarizes the current fundamental knowledge about biofilm adhesion and control.

In a biological denitrification system for water and wastewater treatment, an external carbon source (electron donor) is usually needed to generate dedicated microbial communities if intrinsic organic substances are insufficient. Alternative sources of electron donors, especially inorganic donors, are becoming more and more attractive in order to replace or reduce carbon use. In this article, inorganic electron donors, i.e. zero-valent iron, ferrous ion, sulphur and hydrogen are reviewed. While carbon dioxide (greenhouse gas) is produced when organic electron donors are used, inorganic electron donors have the potential advantages to reduce a plant's carbon footprint, and prevent carbon eluting out of the system, as occurs with heterotrophic processes. While sulphur and hydrogen are promising for nitrate removal in terms of reaction kinetics and economical feasibility, zero-valent iron and ferrous ion show potential to be utilized as a supplement to heterotrophic denitrification, where it is anticipated that synergistic effects would occur with autotrophic and heterotrophic denitrification, and thus external carbon consumption can be reduced.

With climate change, population growth, and water scarcity, there is a growing demand for a sustainable approach to managing water resources. Ozonation followed by biologically active filtration (BAF) recently has drawn interest because of the synergistic effects that enhance performance and reduce operating costs associated with media replacement and ozone dosage. To help guide future process design, a comprehensive pilot study was undertaken to investigate operating parameters of the combined ozonation and BAF process. The study started in January 2014 at Hammarby Sjöstadsverk Wastewater Treatment Plant in Stockholm, Sweden; the process included an ozone contactor and biologically active filters. Anthracite and granular activated carbon (GAC) produced similar results in terms of chemical oxygen demand (COD) and ammonia removal, achieving approximately 50% COD removal and reducing ammonia nitrogen to <0.2 mg/L. Ozone plays an important role in oxidizing micropollutants. GAC demonstrated additional polishing effect for residual micropollutants, whereas anthracite showed additional little removal.

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