Treatment of Wastewater With Slow Rate Systems: A Review of Treatment Processes and Plant Functions

Land treatment systems constitute a viable alternative solution for wastewater management in cases where the construction of conventional (mechanical) wastewater treatment plants (WWTPs) are not affordable or other disposal options are not available. They have proven to be an ideal technology for small rural communities, clusters of homes, and small industrial units due to low energy demands and low operation and maintenance costs. In addition, slow rate systems (SRS) may be designed using the “zero discharge” concept. The purpose of this article is to review the current trends and developments in the field of SRS, focusing on those systems in which effluent application is based on plant water requirements. Vegetation has an important role in treatment efficiency through its effects on hydraulic loading rate, nutrient removal, and biomass production. In addition, vegetation may affect the fate of trace elements and the degradation/detoxification of recalcitrant organics. Detailed knowledge of the basic processes involved in wastewater treatment and the factors governing the performance of SRS is fundamental for enhancing treatment efficiency and eliminating potential environmental and health risks. Finally, monitoring performance of SRS and adopting the appropriate management strategies are of paramount importance to maintain treatment efficiency over the a long term.

KEY WORDS:

• land application
• nutrient removal
• organic pollutants
• pathogens
• vegetation

ACKNOWLEDGEMENTS

Funding in support of this review was provided by the Greek National Scholarships Institute. The authors thank Prof. Roubelakis-Angelakis, University of Crete, Prof. Salgot, University of Catalonia, Dr. Tsagarakis, Technical University of Crete, and Prof. Rose, Michigan State University, for their critical review and comments.

Notes

^a Estimation of WUE is based on evapotranspiration losses and aboveground biomass.

^b During 1 September to 31 October, beets were irrigated at 0.85ET.

^c Calculated using data provided in specified reference.

^a From Allen et al. (1998).

^b Edraki et al. (2004).

^{c c} Myers et al. (1999).

^d Gochis and Cuenca (2000).

^e Depending on clone and growing season (J⊘rgensen and Schelde, 2001).

^a Biomass assessed after leaf fall.

^a Ice nucleotide bacteria.

^b Depending on the bulk density of the soil column.

^c Preferential flow has been documented.

^d Cited in Reed et al. (1995).

^a Adapted from Jimenez (2003) and Feachem et al. (1983).