Molecular Investigations into the Microbiology of a Package Biological Nutrient Removal System

Watkins, S.C.1, Watts, J.E.M.1, May E.1, Williams, J.B.2

  1. School of Biological Sciences, University of Portsmouth, Portsmouth, UK,
  2. 2. School of Civil Engineering and Surveying, University of Portsmouth, Portsmouth, UK

Package treatment systems are typically used for isolated sources of commercial, industrial and agricultural waste. As overloaded sewage treatment plants are becoming a frequent problem due to population increases, package systems are emerging as financially viable supporting technology. A package system capable of treating a population equivalent of 100 was installed to perform biological nutrient removal, and physical, chemical and microbiological parameters were assessed. Presented here is an overview of the physico-chemical aspects of the system, alongside a molecular analysis of the microbial populations. Using denaturing gradient gel electrophoresis (DGGE) and sequencing, an indication of the microbial community composition and stability of a this package system was investigated. Molecular analysis provided a rapid estimate of microbial populations and culturable species could be identified by sequence analysis.


Biological nutrient removal, DGGE, package wastewater treatment.


Centralised wastewater treatment works have been in use since the 1800s, and are based on multistage processes which address the overall works capacity for nutrient and solids removal. Multistage processes can be scaled down into smaller package systems, which provide an alternative to large on centralised networks. These smaller independent systems are particularly important as urban expansion and progression in high density living lead to the overloading of large wastewater treatment plants (Metcalf & Eddy, 2003). These package systems can be used for treatment of waste generated by isolated domestic communities, and industrial or agricultural businesses. On a global scale, billions of people lack access to safe, potable water, and satellite package systems are currently being used as strategies for water reclamation and reuse (Massoud et al., 2009), with a view to eventual adoption of widespread use for the production of potable water in developing countries (Gikas & Tchobanoglous, 2009).

Package systems can deliver high levels of secondary treatment, working to stringent discharge consents. Information regarding the biological aspects of package wastewater treatment systems is sparse, as these systems are often analysed in terms of sustainability, economic and social factors (Hellström et al., 2003). Package systems are monitored for process efficiency, however, this tends to be on the basis of minimal required effluent quality (Balkema et al., 2002), and not as a comprehensive study of processes within the treatment unit. However, the use of smaller systems for wastewater treatment presents a number of unique challenges, in combination with the general operational issues associated with larger plants, and warrant more holistic studies in their own right. Generally, a system with a smaller footprint offers less of a ‘buffer’ for environmental factors such as temperature (which can affect microbial communities), and loading pressures, such as unstable flow (which can affect development of biomass) or toxic loads (which can kill or severely disrupt biomass). Sewage control parameters, such as dissolved oxygen (DO) or hydraulic loading, have a greater ‘cause and effect’ impact on a smaller system than a larger one (Lindsay, 2004). Because of these features, the microenvironment that develops in a small system has the potential to encourage the growth of a completely different microbial community to that of a large scale, multi-stage operation plant. As a result of the complexities associated with controlling a small package system, physico chemical and microbial variables within a system are highly changeable (Crites & Tchobanoglous, 1998), and the study of such a system offers insight into a range of chemical and microbiological processes.

Wastewater contains a heterogeneous mixture of microorganisms, on an incredibly complex scale (Seviour, 1999). Advances in the study of microbial ecology and diversity are very important to wastewater treatment, because the design of these systems is largely based on empirical data (Wagner, 2005), yet we know that many mechanisms of treatment are very fundamentally grounded in microbiology. The in depth study of microbial community dynamics represents a progression for the study of wastewater treatment, which can only be supported with thorough interrogation of all aspects of wastewater treatment systems – physical, chemical and biological.

In this study we report an overview of the physico-chemical characteristics of a small package system and molecular analysis of the microbial community present. Using molecular methods this study aims to examine the total microbial community present in comparison to standard culturable techniques which, although powerful, focus upon a limited number of well characterised populations.

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