Assessment of alternative herbicides for residential sewer root treatment and their effects on downstream treatment plant nitrification.

The conveyance of wastewater in sewer pipes can be severely limited by the growth of plant roots, which can be controlled with herbicides. However, adding herbicides in sewer lines may affect downstream biological wastewater treatment processes. The effects of three herbicides (Dithiopyr, Penoxsulam, and Triclopyr) on the mortality of cottonwood tree roots and on downstream biological nitrification were determined. The results showed that Triclopyr achieved the highest root mortality (96%) followed by Penoxsulam (77%) and Dithiopyr (75%). At concentrations used at the point of application in sewer pipes, all herbicides caused nitrification inhibition and reduction in organic carbon removal in activated sludge. However, no inhibition was observed at the more diluted concentrations approximately equal to levels that may reach the wastewater treatment facility. Overall, Triclopyr appears to be the best performing herbicide with the highest root kill.

CFD for wastewater treatment: an overview.

Computational fluid dynamics (CFD) is a rapidly emerging field in wastewater treatment (WWT), with application to almost all unit processes. This paper provides an overview of CFD applied to a wide range of unit processes in water and WWT from hydraulic elements like flow splitting to physical, chemical and biological processes like suspended growth nutrient removal and anaerobic digestion. The paper's focus is on articulating the state of practice and research and development needs. The level of CFD's capability varies between different process units, with a high frequency of application in the areas of final sedimentation, activated sludge basin modelling and disinfection, and greater needs in primary sedimentation and anaerobic digestion. While approaches are comprehensive, generally capable of incorporating non-Newtonian fluids, multiphase systems and biokinetics, they are not broad, and further work should be done to address the diversity of process designs. Many units have not been addressed to date. Further needs are identified throughout, but common requirements include improved particle aggregation and breakup (flocculation), and improved coupling of biology and hydraulics.

Optimization of activated sludge designs using genetic algorithms.

We describe a framework in which a genetic algorithm (GA) and a static activated sludge (AS) treatment plant design model (WRC AS model) are used to identify low cost activated sludge designs that meet specified effluent limits (e.g. for BOD, N, and P). Once the user has chosen a particular process (Bardenpho, Biodenipho, UCT or SBR), this approach allows the parameterizations for each AS unit process to be optimized systematically and simultaneously. The approach is demonstrated for a wastewater treatment plant design problem and the GA-based performance is compared to that of a classical nonlinear optimization approach. The use of GAs for multiobjective problems such as AS design is demonstrated and their application for reliability-based design and alternative generation is discussed.