Adaptation in hindsight: dynamics and drivers shaping urban wastewater systems.

Well-planned urban infrastructure should meet critical loads during its design lifetime. In order to proceed with design, engineers are forced to make numerous assumptions with very little supporting information about the development of various drivers. For the wastewater sector, these drivers include the future amount and composition of the generated wastewater, effluent requirements, technologies, prices of inputs such as energy or chemicals, and the value of outputs produced such as nutrients for fertilizer use.

Intermittent operation of ultra-low pressure ultrafiltration for decentralized drinking water treatment.

River water was treated by ultrafiltration at a relatively low transmembrane pressure (40 mbar). As observed before, flux stabilization occurred after several days of operation although no back-flushing or cross flow was applied. Interruptions in flux were applied by temporary offset of the transmembrane pressure.

Automatic reactor model synthesis with genetic programming.

Successful modeling of wastewater treatment plant (WWTP) processes requires an accurate description of the plant hydraulics. Common methods such as tracer experiments are difficult and costly and thus have limited applicability in practice; engineers are often forced to rely on their experience only. An implementation of grammar-based genetic programming with an encoding to represent hydraulic reactor models as program trees should fill this gap: The encoding enables the algorithm to construct arbitrary reactor models compatible with common software used for WWTP modeling by linking building blocks, such as continuous stirred-tank reactors.

Is modeling of biological wastewater treatment a mature technology?

Based on three case studies it is demonstrated that the application of mathematical models in biological wastewater treatment has not yet reached its full potential. Model structure uncertainty and correlation of uncertain parameter values make up the first case. The combination of biokinetic and hydraulic models relates to the second case.

Modelling biocide leaching from facades.

Biocides leach from facades during rain events and subsequently enter the aquatic environment with storm water. Little is known about the losses of an entire settlement, since most studies referred to wash-off experiments conducted under laboratory conditions. Their results show a fast decrease of concentrations in the beginning, which subsequently slows down.

Identification of industrial wastewater by clustering wastewater treatment plant influent ultraviolet visible spectra.

A procedure is proposed which allows the detection of industrial discharge events at the inlet of a wastewater treatment plant without the need for measurements performed at the industry, for special equipment and for exact knowledge of the industrial sewage. By performing UV/Vis measurements at the inlet of a plant and analyzing them with a two-staged clustering method consisting of the self-organizing map algorithm and the Ward clustering method, typical sewage clusters can be found. In an experiment performed at a mid-sized Swiss plant, one cluster of a cluster model with five clusters could be attributed to an industrial laundry.

Using reactive tracers to detect flow field anomalies in water treatment reactors.

The hydraulics of water and wastewater treatment reactors has a major impact on their performance and control. The residence time distribution as a measure for the hydraulics represents macroscopic mixing in an integrated way with no spatial information. However, with regard to optimal sensor location for process control and for process optimisation measures, spatial information about macro-mixing is helpful.

Effects of aeration patterns on the flow field in wastewater aeration tanks.

Due to the high energy input of aeration, the spatial distribution of air diffusers largely determines the flow field in aeration tanks. This has consequences on the efficiency of the aeration system, the performance of the aeration tank and on tank operation and control. This paper deals with these effects applying both Computational Fluid Dynamics (CFD) enhanced with a biokinetic model and full scale validation using velocity and reactive tracer measurements with high temporal and spatial resolution.

Global sensitivity analysis in wastewater treatment plant model applications: prioritizing sources of uncertainty.

This study demonstrates the usefulness of global sensitivity analysis in wastewater treatment plant (WWTP) design to prioritize sources of uncertainty and quantify their impact on performance criteria. The study, which is performed with the Benchmark Simulation Model no. 1 plant design, complements a previous paper on input uncertainty characterisation and propagation (Sin et al.

Struvite precipitation from urine - Influencing factors on particle size.

Struvite crystallisation is a fast and reliable phosphorus removal and recovery process for concentrated waste streams - such as hydrolysed human urine. In order to optimise P-elimination efficiency, it is beneficial to obtain larger particle sizes: they are easier to separate and less prone to wash-out than smaller particles. This paper presents the results of a study on the effect of process parameters on particle size in a single step struvite precipitation.

Nitrification and me - a subjective review.

Based on the subjective experience of the author it is discussed how the nitrification processes served as an important basis for the development of today's understanding and mathematical models for many wastewater treatment processes (activated sludge, biofilm reactors) and self-purification processes in rivers. Besides being an important process for the protection of receiving waters, nitrification served as a proxy for the understanding of the behavior of a narrowly defined group of microorganisms growing on known substrates under environmental conditions. Until the upcoming of readily available microbial genetic techniques, nitrification was the single most studied microbial process in environmental engineering.

Compartmental models for continuous flow reactors derived from CFD simulations.

Reactor modeling is of major interest in environmental technology. In this context, new contaminants with higher degradation requirements increase the importance of reactor hydraulics. CFD (Computational Fluid Dynamics) may meet this challenge but is expensive for everyday use.

Uncertainty analysis in WWTP model applications: a critical discussion using an example from design.

This study focuses on uncertainty analysis of WWTP models and analyzes the issue of framing and how it affects the interpretation of uncertainty analysis results. As a case study, the prediction of uncertainty involved in model-based design of a wastewater treatment plant is studied. The Monte Carlo procedure is used for uncertainty estimation, for which the input uncertainty is quantified through expert elicitation and the sampling is performed using the Latin hypercube method.

Global sensitivity analysis for model-based prediction of oxidative micropollutant transformation during drinking water treatment.

This study quantifies the uncertainty involved in predicting micropollutant oxidation during drinking water ozonation in a pilot plant reactor. The analysis is conducted for geosmin, methyl tert-butyl ether (MTBE), isopropylmethoxypyrazine (IPMP), bezafibrate, beta-cyclocitral and ciprofloxazin. These compounds are representative for a wide range of substances with second order rate constants between 0.

Underestimation of uncertainty in statistical regression of environmental models: influence of model structure uncertainty.

As the quality of sensors increases, systematic discrepancies between measurements and model outputs become more apparent Applying regression type analysis in these cases leads to autocorrelated residuals, biased parameter estimates, and underestimation of uncertainty. This paper examines how parameter estimates are affected by model structure uncertainty for an application from wastewater treatment. A Monod model is fitted to synthetic data generated by a reference system exhibiting predefined Tessier kinetics and a known error process.

Sources of parameter uncertainty in predicting treatment performance: the case of preozonation in drinking water engineering.

This study investigates the factors that determine parameter uncertainty when applying predefined, existing models to predict the performance of a full scale treatment system from environmental engineering. The analysis is performed for ozonation of surface water, a technology applied in drinking water treatment for disinfection and oxidation of micropollutants. The pseudo first order rate constant of ozone decay k(O3) is characterized as a time dependent parameter and estimated from data obtained from three experimental setups representing upscaling stages in engineering design.

Uncertainty in prediction of disinfection performance.

Predicting the disinfection performance of a full-scale reactor in drinking water treatment is associated with considerable uncertainty. In view of quantitative risk analysis, this study assesses the uncertainty involved in predicting inactivation of Cryptosporidium parvum oocysts for an ozone reactor treating lake water. A micromodel is suggested which quantifies inactivation by stochastic sampling from density distributions of ozone exposure and lethal ozone dose.

The behaviour of pharmaceuticals and heavy metals during struvite precipitation in urine.

Separating urine from wastewater at the source reduces the costs of extensive wastewater treatment. Recovering the nutrients from urine and reusing them for agricultural purposes adds resource saving to the benefits. Phosphate can be recovered in the form of struvite (magnesium ammonium phosphate).

Estimating sewer leakage from continuous tracer experiments.

Direct measurements of sewer leakage with continuous dosing of tracers are often considered too imprecise for practical applications. However, no mathematical framework for data analysis is reported in literature. In this paper, we present an improved experimental design and data analysis procedure together with a comprehensive framework for uncertainty assessment.

Discrete event simulation for exploring strategies: an urban water management case.

This paper presents a model structure aimed at offering an overview of the various elements of a strategy and exploring their multidimensional effects through time in an efficient way. It treats a strategy as a set of discrete events planned to achieve a certain strategic goal and develops a new form of causal networks as an interfacing component between decision makers and environment models, e.g.

Struvite precipitation thermodynamics in source-separated urine.

Struvite (MgNH(4)PO(4).6H(2)O) precipitation eliminates phosphate efficiently from urine, a small but highly concentrated stream in the total flux of domestic wastewater. Precipitation experiments with hydrolysed urine evaluated the solubility product of struvite.

Exploring temporal variations of oxygen saturation constants of nitrifying bacteria.

Activated sludge models (ASM) are generally accepted as state-of-the-art in modeling wastewater treatment plants. In this paper, we assess the temporal variability of an ASM parameter-the oxygen half-saturation constant of autotrophic bacteria (K(O),(AUT)). A series of respirometric experiments is performed for conventional activated sludge and sludge from a membrane bioreactor.

Confronting limitations: new solutions required for urban water management in Kunming City.

Despite continuous investment and various efforts to control pollution, urban water environments are worsening in large parts of the developing world. In order to reveal potential constraints and limitations of current practices of urban water management and to stimulate proactive intervention, we conducted a material flow analysis of the urban water system in Kunming City. The results demonstrate that the current efficiency of wastewater treatment is only around 25% and the emission of total phosphorous from the city into its receiving water, Dianchi Lake, is more than 25 times higher than its estimated tolerance.

Decay processes of nitrifying bacteria in biological wastewater treatment systems.

A knowledge of the decay rates of autotrophic bacteria is important for reliably modeling nitrification in activated sludge plants. The introduction of nitrite to activated sludge models also requires the separate determination of the kinetics of ammonia- and nitrite-oxidizing bacteria. Batch experiments were carried out in order to study the effects of different oxidiation-reduction potential conditions and membrane separation on the separate decay of these bacteria.

Evolution of a wastewater treatment plant challenges traditional design concepts.

Traditional design and upgrade concepts for wastewater treatment plants (WWTPs) are based on the forecasting of load parameters over a period of 25-40 years. This approach is adequate as long as the environment of a WWTP is stable or predictable over this long time period. However, these conditions are usually not met, as the catchment area, discharge requirements, available technology and institutional conditions of a WWTP may change drastically over time.