Henryk Melcer

Perspectives on modelling micropollutants in wastewater treatment plants

Models for predicting the fate of micropollutants (MPs) in wastewater treatment plants (WWTPs) have been developed to provide engineers and decision-makers with tools that they can use to improve their understanding of, and evaluate how to optimize, the removal of MPs and determine their impact on the receiving waters. This paper provides an overview of such models, and discusses the impact of regulation, engineering practice and research on model development. A review of the current status of MP models reveals that a single model cannot represent the wide range of MPs that are present in wastewaters today, and that it is important to start considering classes of MPs based on their chemical structure or ecotoxicological effect, rather than the individual molecules. This paper identifies potential future research areas that comprise (i) considering transformation products in MP removal analysis, (ii) addressing advancements in WWTP treatment technologies, (iii) making use of common approaches to data acquisition for model calibration and (iv) integrating ecotoxicological effects of MPs in receiving waters.

Rethinking wastewater characterisation methods for activated sludge systems – a position paper

Increasingly stringent effluent limits and an expanding scope of model system boundaries beyond activated sludge has led to new modelling objectives and consequently to new and often more detailed modelling concepts. Nearly three decades after the publication of Activated Sludge Model No1 (ASM1), the authors believe it is time to re-evaluate wastewater characterisation procedures and targets. The present position paper gives a brief overview of state-of-the-art methods and discusses newly developed measurement techniques on a conceptual level. Potential future paths are presented including on-line instrumentation, promising measuring techniques, and mathematical solutions to fractionation problems. This is accompanied by a discussion on standardisation needs to increase modelling efficiency in our industry.

Modeling of volatile organic contaminants in trickling filter systems

Despite the widespread use of trickling filters, there has been minimal investigation of the fate of volatile organic contaminants (VOCs) in such systems. A model describing the fate of VOCs in trickling filters is described. The removal of VOCs was investigated in a pilot-scale trickling filter receiving a feed of sewage dosed with a constant concentration of selected VOCs. Increasing hydraulic loading tended to increase the proportion of influent VOCs found in the effluent. Imposing effluent recycle also increased the fraction of VOCs found in the effluent but also decreased the fraction stripped and increased the fraction that was biodegraded. The values of the biodegradation coefficient, K b , were found to be reproducible and affected by a combination of high hydraulic loading rate and effluent recycle.

Modelling and characterization of primary settlers in view of whole plant and resource recovery modelling

Characterization and modelling of primary settlers have been neglected pretty much to date. However, whole plant and resource recovery modelling requires primary settler model development, as current models lack detail in describing the dynamics and the diversity of the removal process for different particulate fractions. This paper focuses on the improved modelling and experimental characterization of primary settlers. First, a new modelling concept based on particle settling velocity distribution is proposed which is then applied for the development of an improved primary settler model as well as for its characterization under addition of chemicals (chemically enhanced primary treatment, CEPT). This model is compared to two existing simple primary settler models (Otterpohl and Freund; Lessard and Beck), showing to be better than the first one and statistically comparable to the second one, but with easier calibration thanks to the ease with which wastewater characteristics can be translated into model parameters. Second, the changes in the activated sludge model (ASM)-based chemical oxygen demand fractionation between inlet and outlet induced by primary settling is investigated, showing that typical wastewater fractions are modified by primary treatment. As they clearly impact the downstream processes, both model improvements demonstrate the need for more detailed primary settler models in view of whole plant modelling.

Aromatic VOC emissions from a municipal sewer interceptor

Municipal and industrial sewers have come under increased regulatory scrutiny as sources of volatile organic compound (VOC) emissions to the ambient atmosphere. A well-ventilated municipal sewer interceptor that receives significant quantities of VOC-laden industrial wastewater was studied to quantify VOC emissions. Headspace outgassing rates across four manhole covers were as high as 2300 m 3 /h. Emissions were greatest for toluene, approaching 100 g/h from a single manhole cover at the mid-point of the 24-hour event. Significant diurnal and weekday/weekend trends were observed. Emissions from a single manhole cover rivaled or exceeded those summed over aerated grit chambers and aeration basins at four large municipal wastewater treatment facilities in Southern Ontario. The primary source of VOC stripping was observed to be a series of large drop structures, with aromatic VOC stripping efficiencies ranging from 25 to 38% across two drops. Finally, an existing model that predicts VOC emissions from sewers was observed to reasonably predict measured stripping efficiencies. An important conclusion of this study is that large fractions of VOCs may be removed from wastewater and emitted to the ambient atmosphere prior to entering a downstream treatment facility.

Control of VOC emissions from sewers: A multi-parameter assessment

A computational model is described which facilitates multi-parameter analyses of VOC emissions from sewers. The model, CORAL+, was used to simulate more than 3.6 million combinations of five system parameters, including sewer channel slope, relative depth of flow, pipe diameter, Henry9s law coefficient, and headspace ventilation rate. Lumped results were analyzed using a graphical frequency array approach to identify parameter combinations that lead to potential VOC emission hot spots. Additional modeling was completed to provide examples of passive VOC emission reductions through control of system parameters. Computational results provide information related to combinations of parameters that either never or always lead to potential VOC emission hot spots, independent of the values associated with all other parameters. Results indicate that the common assumption of infinite ventilation can lead to significant overestimates of VOC emissions, and that controlled headspace ventilation can be used to reduce VOC emissions by an order of magnitude or more. This may be of significance with respect to reducing emissions from on-site industrial sewers by maintaining biodegradable VOCs in solution prior to discharge to a downstream biological treatment system. Results also suggest that VOC emissions are highly sensitive to wastewater flow rate, increasing as flow rate decreases. This is an important observation with respect to the fact that some municipalities encourage industrial discharges at night for purposes of flow equalization.