D. Brdjanovic

Biological wastewater treatment: Principles, modelling and design

For information on the online course in Biological Wastewater Treatment from UNESCO-IHE, visit: http://www.iwapublishing.co.uk/books/biological-wastewater-treatment-online-course-principles-modeling-and-design Over the past twenty years, the knowledge and understanding of wastewater treatment have advanced extensively and moved away from empirically-based approaches to a first principles approach embracing chemistry, microbiology, physical and bioprocess engineering, and mathematics. Many of these advances have matured to the degree that they have been codified into mathematical models for simulation with computers. For a new generation of young scientists and engineers entering the wastewater treatment profession, the quantity, complexity and diversity of these new developments can be overwhelming, particularly in developing countries where access is not readily available to advanced level tertiary education courses in wastewater treatment. Biological Wastewater Treatment addresses this deficiency. It assembles and integrates the postgraduate course material of a dozen or so professors from research groups around the world that have made significant contributions to the advances in wastewater treatment. The book forms part of an internet-based curriculum in biological wastewater treatment which also includes: * Summarized lecture handouts of the topics covered in book * Filmed lectures by the author professors * Tutorial exercises for students self-learning Upon completion of this curriculum the modern approach of modelling and simulation to wastewater treatment plant design and operation, be it activated sludge, biological nitrogen and phosphorus removal, secondary settling tanks or biofilm systems, can be embraced with deeper insight, advanced knowledge and greater confidence.

Anticipating the next century of wastewater treatment

Advances in activated sludge sewage treatment can improve its energy use and resource recovery Rapid urbanization and industrialization in the 19th century led to unhealthy environments and wide-spread epidemic diseases. In response, research was undertaken that led to the development of sanitation technology. Exactly 100 years since the activated sludge process was presented (1), it is still at the heart of current sewage treatment technology. Activated sludge is a mixture of inert solids from sewage combined with a microbial population growing on the biodegradable substrates present in the sewage. The settling and recycling of sludge inside treatment plants was the invention of Ardern and Lockett. The current demands from a rapidly growing human population and the need for a more sustainable society are pushing forward new developments for sewage handling. These developments have two main drivers: general process improvements and the contribution to the recycling of resources (2, 3).

Biological phosphate removal processes

Abstract Biological phosphate removal has become a reliable and well-understood process for wastewater treatment. This review describes the historical development of the process and the most important microbiological and process-engineering aspects. From a microbiological point of view, the role of␣poly(hydroxyalkanoates) as storage material in a dynamic process and the use of polyphosphate as an energy reserve are the most important findings. From a process-engineering point of view, the study of biological phosphate removal has shown that highly complex biological processes can be designed and controlled, provided that the importance of the prevailing microbiological ecological processes is recognised.

Modeling COD, N and P removal in a full-scale wwtp Haarlem Waarderpolder

Abstract In this study the following was evaluated: (a) application of a complex activated sludge model on a full-scale plant (Phostrip ® -like process), (b) influent and sludge characterization procedures for bio-P modeling, (c) the use of batch tests for model evaluation and (d) different alternative BPR process configurations (A/O, UCT and BCFS ® ). An integrated model for aerobic and denitrifying biological phosphorus removal (Delft bio-P model) replaced the module for P removal of ASM No. 2 and was combined with retained equations for COD and N conversion of the ASM No 2. This combined model proved well capable of describing the wastewater treatment plant (wwtp) Haarlem Waarderpolder with adjustment of only three (out of the sixty) default parameters. Some of batch tests were satisfactorily described by the model too. Batch tests proved as a useful tool for sludge characterization and model validation. The standard Dutch procedure for influent and sludge characterization proved satisfactory for the model construction. Modeling of alternative BPR process configuration showed that good P removal was achieved by all three alternative process configurations, by the latest one with comparatively lowest construction and operational costs (lower building costs and no acetate addition). Valuable experience from practical application of the model was obtained; study indicated where the model should be improved; the plant operation and treatment processes were better understood and plant performance was further optimized.

Influence of temperature on biological phosphorus removal: process and molecular ecological studies

Abstract This paper describes the impact of long-term (weeks) temperature changes on stoichiometry and kinetics of the anaerobic and aerobic phases of the biological phosphorus removal process. Steady state conversion of relevant compounds for biological phosphorus removal was studied at 20, 30, 20, 10 and 5°C, following chronological order. Integrated in the process study, two methods (electron-microscopy and dry denaturing gradient gel electrophoresis) were applied to investigate the complexity of the bacterial community of biological phosphorus removing sludge cultivated at different temperatures. The coefficient for metabolic conversions obtained from long-term temperature tests was similar to the temperature coefficient observed in short-term (hours) tests ( θ =1.085 versus θ =1.078, respectively).Temperature had a moderate impact on the aerobic P-uptake process rate ( θ =1.031) during long-term tests. However, a strong temperature effect on other metabolic processes of the aerobic phase, such as polyhydroxyalkanoate consumption ( θ =1.163), oxygen uptake ( θ =1.090) and growth ( θ >1.110), was observed. Different temperature coefficients were obtained for the aerobic phase from long-term and short-term tests, probably due to a change in population structure. This change was also visible from molecular ecological studies. The different temperature coefficient found for P-uptake compared to the other metabolic processes of the aerobic phase underlines that, in complex processes such as BPR, it is dangerous to draw conclusions from easily observable parameters (like phosphate) only. Such consideration can easily lead to underestimation of the temperature dependency of other metabolic processes of the aerobic phase of BPR.

The dynamic effects of potassium limitation on biological phosphorus removal

Abstract A full-scale sewage treatment plant designed for biological phosphorus removal may experience short- or long-term shortage in potassium of the influent. In this study, using an anaerobic-aerobic sequenced batch reactor system, inoculation sludge from laboratory-, pilot- and full-scale phosphorus removal plants was exposed to different potassium-phosphorus ratios in the influent. By simulating the conditions which may occur in practice, it was shown that potassium is an essential factor in biological phosphorus removal processes. When the system was exposed to severe shortage of potassium in the influent: (a) phosphorus removal was absent, (b) polyphosphate concentration in the biomass decreased exponentially due to sludge wasting and (c) the anaerobic phosphorus release and the related acetate uptake was only affected after several days of potassium absence, likely due to insufficient content of polyphosphate in the biomass to allow full acetate uptake under anaerobic conditions. In contrast, the system achieved complete phosphorus removal when potassium was present in excess amounts.

Minimal aerobic sludge retention time in biological phosphorus removal systems

The methodology for determination of the minimally required aerobic sludge retention time (SRTminaer) in biological phosphorus removal (BPR) systems is presented in this article. Contrary to normal biological conversions, the BPR process is not limited by a SRTmin resulting from the maximum growth rate of the organisms. This is because the aerobic SRT should be long enough to oxidize the amount of poly-hydroxy-alkanoates (PHA) stored in the anaerobic phase. This means that the SRTminaer will primarily depend on the PHA conversion kinetics and the maximal achievable PHA content in the cell (storage capacity). The model for the prediction of the minimally required aerobic SRT as a function of kinetic and process parameters was developed and compared with experimental data used to evaluate several operational aspects of BPR in a sequencing batch reactor (SBR) system. The model was proved as capable of describing them satisfactorily.Copyright 1998 John Wiley & Sons, Inc.

Anammox cultivation in a closed sponge-bed trickling filter

A feasibility study was carried out to assess the cultivation of Anammox bacteria in lab-scale closed sponge-bed trickling filter (CSTF) reactors, namely: CSTF-1 at 20°C and CSTF-2 at 30°C. Stable conditions were reached from day 66 in CSTF-2 and from day 104 in CSTF-1. The early stability of CSTF-2 is attributable to the influence of temperature; nevertheless, by day 405, the nitrogen removal performed by CSTF-1 increased up to similar values of CSTF-2. The maximum total nitrogen removal efficiency was 82% in CSTF-1 and 84% in CSTF-2. After more than 400 days of operation, CSTF-1 and CSTF-2 were capable to attain a total nitrogen removal efficiency of 74±5% and 78±4% with a total nitrogen conversion rate of 1.52 and 1.60kg-N/m(sponge)(3)d, respectively. The proposed technology could be a suitable alternative for mainstream nitrogen removal in post-treatment units via the Anammox conversion pathway.

Effects of organic carbon source, chemical oxygen demand/N ratio and temperature on autotrophic nitrogen removal

To assess the feasibility of the Anammox process as a cost-effective post-treatment step for anaerobic sewage treatment, the simultaneous effects of organic carbon source, chemical oxygen demand (COD)/N ratio, and temperature on autotrophic nitrogen removal was studied. In batch experiments, three operating conditions were evaluated at 14, 22 and 30 °C, and at COD/N ratios of 2 and 6. For each operating condition, containing 32 ± 2 mg NH4(+)-N/L and 25 ± 2 mg NO2(-)-N/L, three different substrate combinations were tested to simulate the presence of readily biodegradable and slowly biodegradable organic matter (RBCOD and SBCOD, respectively): (i) acetate (RBCOD); (ii) starch (SBCOD); and (iii) acetate + starch. The observed stoichiometric NO2(-)-N/NH4(+)-N conversion ratios were in the range of 1.19-1.43, and the single or simultaneous presence of acetate and starch did not affect the Anammox metabolism. High Anammox nitrogen removal was observed at 22 °C (77-84%) and 30 °C (73-79%), whereas there was no nitrogen removal at 14 °C; the Anammox activity was strongly influenced by temperature, in spite of the COD source and COD/N ratios applied. These results suggest that the Anammox process could be applied as a nitrogen removal post-treatment for anaerobic sewage systems in warm climates.

Occurrence of PAOI in a low temperature EBPR system

The occurrence of Accumulibacter Type I (a known phosphorus-accumulating organism, PAO) has received increased attention due to the potential operating benefits associated with their denitrifying activity in enhanced biological phosphorus removal (EBPR) wastewater treatment plants. In this study, after a shift from an enriched glycogen-accumulating organism (GAO) culture (competitors of PAO) to a PAO-enriched system, Accumulibacter Type I (PAO I) became dominant in an anaerobic-aerobic EBPR system fed with acetate and operated at 10°C with a net aerobic solids retention time (SRT) of 6 d. Since Accumulibacter Type II (PAO II) were not detected, the low temperature in combination with the net aerobic SRT applied appeared to have suppressed their growth as well. The stoichiometry of PAO I was in agreement with previous metabolic models, suggesting that it was the main PAO organisms present in previous studies operated under similar conditions. Moreover, under poly-P limiting conditions, PAO I were unable to switch to a GAO-like metabolism at low temperatures. These results contribute to increase the understanding of the physiology, microbial metabolism and microbial ecology of PAO I.