Processes and modeling of hydrolysis of particulate organic matter in aerobic wastewater treatment--a review.

Carbon cycling and the availability of organic carbon for nutrient removal processes are in most wastewater treatment systems restricted by the rate of hydrolysis of slowly biodegradable (particulate) organic matter. To date, the mechanisms of hydrolysis are not well understood for complex substrates and mixed populations. Most mathematical models use a simple one-step process to describe hydrolysis. In this article, mechanisms of hydrolysis and mathematical models to describe these processes in wastewater treatment processes are reviewed. Experimental techniques to determine mechanisms of hydrolysis and rate constants are discussed.

Dissemination of regional rainfall analysis in design and analysis of urban drainage at un-gauged locations.

A research program in Denmark on statistical modelling of rainfall has resulted in a model for regional distribution of rainfall extremes. The results show that extreme rainfalls critical to the hydraulic function of urban drainage systems and the pollution discharge are subject to a significant regional variation of extreme rainfalls throughout the country. This has implications for design and analysis of all practical problems related to urban drainage, since the rainfall data so far recommended as input to engineering analyses underestimates the problems. Consequently, the Danish Water Pollution Control Committee has issued a statement recommending a new engineering practice. The dissemination of the research results proved to be difficult due to lack of understanding of the concepts of the new paradigm by practitioners. The traditional means of communication was supplemented by user-friendly spreadsheets and easy access to rainfall data as well as giving courses on the new paradigm. This has eased the implementation of the new concepts greatly.

Integrated urban drainage, status and perspectives.

This paper summarises the status of urban storm drainage as an integrated professional discipline, including the management-policy interface, by which the goals of society are implemented. The paper assesses the development of the discipline since the INTERURBA conference in 1992 and includes aspects of the papers presented at the INTERURBA-II conference in 2001 and the discussions during the conference. Tools for integrated analysis have been developed, but there is less implementation than could be expected. That is due to lack of adequate knowledge about important mechanisms, coupled with a significant conservatism in the business. However, significant integrated analyses have been reported. Most of them deal with the sewer system and the treatment plant, while few incorporate the receiving water as anything but the object of the loads to be minimised by engineering measures up-stream. Important measures are local infiltration, source control, storage basins, local treatment and real time control. New paradigms have been introduced: risk of pollution due to system failure, technology for water reuse, sustainability, new architecture and greener up-stream solutions as opposed to down-stream concrete solutions. The challenge is to combine the inherited approaches with the new approaches by flexibility and adaptability.

Analysis of scenarios for sewerage, wastewater treatment and prioritised load on environment from the Greater City of Copenhagen.

The sewer system for the Greater Copenhagen area covers an area of 4460 ha contributing to the runoff. The total area serves in total 8 municipalities, however it is dominated by the areas in the City of Copenhagen proper. The catchments merge into interceptors, which feed two large treatment plants. The effluent from the two treatment plants discharges during dry weather to Oresund, the sound between Denmark and Sweden. This large system has been analysed for selected scenarios with respect to handling runoff in an optimal way in order to minimise the loads on the most sensitive receiving waters and optimising treatment plant performance.

Kinetic start-up performance of two large treatment plants for nutrient removal.

In 1987 an action plan was passed in the Danish Parliament demanding a considerable reduction of the discharge of nutrients to the aquatic environment in Denmark. Consequently, the two largest wastewater treatment plants in the Copenhagen area had to be upgraded to include nutrient removal. For more than 8 years an extensive effort has been made to determine an optimum solution for this upgrading from a technical and financial point of view. The work included six years of comprehensive pilot plant investigations with the aim of thoroughly studying and interpreting the kinetics of the processes involved. The investigations revealed valuable information particularly concerning limitations of the nitrification process. Consequently, the investigations contributed to an expectation of no unforeseen problems during the implementation of the upgraded plants. This paper presents the results of the start-up of the two full-scale plants with the main emphasis laid on the kinetic performance in relation to the information achieved from the pilot tests. The results showed that the start-up of the full scale plants proceeded with great accuracy as expected from the investigations. Accordingly, the implementation of the plants was carried out successfully, ending an era of more than 10 years in total.

Possible complication regarding phosphorus removal with a continuous flow biofilm system: diffusion limitation.

Diffusion limitation of phosphate possibly constitutes a serious problem regarding the use of a biofilm reactor for enhanced biological phosphorus removal. A lab-scale reactor for simultaneous removal of phosphorus and nitrate was operated in a continuous alternating mode of operation. For a steady-state operation with excess amounts of carbon source (acetate) during the anaerobic phase, the same amount of phosphate was released during the anaerobic phase as was taken up during the anoxic phase. The measured phosphorus content of the biomass that detached during backwash after an anoxic phase was low, 2.4 +/- 0.4% (equal to 24 +/- 4 mg P/g TS). A simplified computer model indicated the reason to be phosphate diffusion limitation and the model revealed a delicate balance between the obtainable phosphorus contents of the biomass and operating parameters, such as backwash interval, biofilm thickness after backwash, and phase lengths. The aspect of diffusion is considered of crucial importance when evaluating the performance of a biofilter for phosphate removal.

Stability of a lab-scale biofilm for simultaneous removal of phosphorus and nitrate.

A lab-scale biofilm reactor for simultaneous removal of phosphorus and nitrate was operated for one and a half years. Despite using only well defined synthetic wastewater and well defined operation, the activity varied significantly over the months. It was speculated that microbial population shifts were causing this phenomenon. This could also explain a sudden break down of the process following a slight change in the operation. Over shorter periods of time (time-scale: days), the biofilm could be considered stable enough to perform series of comparable batch experiments. Batch experiments with different start concentrations of acetate, nitrate or phosphate were conducted. These verified 0.5 and 0 order removal rates in the bulk water depending on the concentration. This was taken as an indication of a zonation of the biofilm. Due to the measured variability in the activity and due to the importance of the history of the bacteria when considering biological P removal, on-line measurements are strongly recommended for research on this subject. Microbial characterisation methods are recommended as an assisting tool in further research.