M.K. de Kreuk

Pilot-scale evaluation of anammox-based mainstream nitrogen removal from municipal wastewater

Autotrophic nitrogen removal in the mainstream wastewater treatment process is suggested to be a prerequisite of energy autarkic wastewater treatment plants (WWTP). Whilst the application of anammox-related technologies in the side-stream is at present state of the art, the feasibility of this energy-efficient process at mainstream conditions is still under development. Lower operating temperature and ammonium concentration, together with required high nitrogen removal efficiency, represent the main challenges to face in order to reach this appealing new frontier of the wastewater treatment field. In this study, we report the evaluation of the process in a plug-flow granular sludge-based pilot-scale reactor (4 m3) continuously fed with the actual effluent of the A-stage of the WWTP of Dokhaven, Rotterdam. The one-stage partial nitritation–anammox system was operated for more than 10 months at 19 ± 1°C. Observed average N-removal and ammonium conversion rates were comparable or higher than those of conventional N-removal systems, with 182 ± 46 and 315 ± 33 mg-N L−1 d−1, respectively. Biochemical oxygen demand was also oxidized in the system with an average removal efficiency of 90%. Heterotrophic biomass grew preferentially in flocs and was efficiently washed out of the system. Throughout the experimentation, the main bottleneck was the nitritation process that resulted in nitrite-limiting conditions for the anammox conversion. Anammox bacteria were able to grow under mainstream WWTP conditions and new granules were formed and efficiently retained in the system.

Behavior of polymeric substrates in an aerobic granular sludge system.

Particulate and slowly biodegradable substrates form an important fraction of industrial wastewater and sewage. To study the influence of suspended solids and colloidal substrate on the morphology and performance of aerobic granular sludge, suspended and soluble starch was used as a model substrate. Degradation was studied using microscopy, micro-electrode measurements, batch experiments and long term laboratory scale reactor operation. Starch was removed by adsorption at the granule surface, followed by hydrolysis and consumption of the hydrolyzed products. Aerobic granules could be maintained on starch as sole influent carbon source, but their structure was filamentous and irregular. It is hypothesized that this is related to the low starch hydrolysis rates, leading to available substrate during the aeration period (extended feast period) and resulting in increased substrate gradients over the granules. The latter induces a less uniform granule development. Starch adsorbed and was consumed at the granule surface instead of being accumulated inside the granules as occurs for soluble substrates. Therefore the simultaneous denitrification efficiencies remained low. Moreover, many protozoa and metazoans were observed in laboratory reactors as well as in pilot- and full-scale Nereda(®) reactors, indicating an important role in the removal of suspended solids too.

Aerobic Granular Sludge

Aerobic Granular Sludge has recently received growing attention by researchers and technology developers, worldwide. Laboratory studies and preliminary field tests led to the conclusion that granular activated sludge can be readily established and profitably used in activated sludge plants, provided ‘correct’ process conditions are chosen. But what makes process conditions ‘correct’? And what makes granules different from activated sludge flocs? Answers to these question are offered in Aerobic Granular Sludge. Major topics covered in this book include: Aerobic Granular Sludge provides up-to-date information about a rapidly emerging new technology of biological treatment. This title belongs to Water and Environmental Management Series (WEMS) ISBN: 9781843395096 (Print) ISBN: 9781780402055 (eBook)

Quantification of continual anthropogenic pollutants released in swimming pools

Disinfection in swimming pools is often performed by chlorination, However, anthropogenic pollutants from swimmers will react with chlorine and form disinfection by-products (DBPs). DBPs are unwanted from a health point of view, because some are irritating, while others might be carcinogenic. The reduction of anthropogenic pollutants will lead to a reduction in DBPs. This paper investigates the continual release of anthropogenic pollutants by means of controlled sweat experiments in a pool tank during laboratory time-series experiments (LTS experiments) and also during on-site experiments (OS experiments) in a swimming pool. The sweat released during the OS and LTS experiments was very similar. The sweat rate found was 0.1-0.2 L/m(2)/h at water temperatures below 29 °C and increased linearly with increasing water temperatures to 0.8 L/m(2)/h at 35 °C. The continual anthropogenic pollutant release (CAPR) not only consisted of sweat, particles (mainly skin fragments and hair) and micro-organisms, but also sebum (skin lipids) has to be considered. The release of most components can be explained by the composition of sweat. The average release during 30 min of exercise is 250 mg/bather non-purgeable organic carbon (NPOC), 77.3 mg/bather total nitrogen (TN), 37.1 mg/bather urea and 10.1 mg/bather ammonium. The release of NPOC cannot be explained by the composition of sweat and is most probably a result of sebum release. The average release of other components was 1.31 × 10(9) # particles/bather (2-50 μm), 5.2 μg/bather intracellular adenosine triphosphate (cATP) and 9.3 × 10(6) intact cell count/bather (iCC). The pool water temperature was the main parameter to restrain the CAPR. This study showed that a significant amount of the total anthropogenic pollutants release is due to unhygienic behaviour of bathers.

Strength characteristics of aerobic granular sludge.

Aerobic granular sludge has a number of advantages over conventional activated sludge flocs, such as cohesive and strong matrix, fast settling characteristic, high biomass retention and ability to withstand high organic loadings, all aspects leading towards a compact reactor system. Still there are very few studies on the strength of aerobic granules. A procedure that has been used previously for anaerobic granular sludge strength analysis was adapted and used in this study. A new coefficient was introduced, called a stability coefficient (S), to quantify the strength of the aerobic granules. Indicators were also developed based on the strength analysis results, in order to categorize aerobic granules into three levels of strength, i.e. very strong (very stable), strong (stable) and not strong (not stable). The results indicated that aerobic granules grown on acetate were stronger (high density: >150 g T SSL(-1) and low S value: 5%) than granules developed on sewage as influent. A lower value of S indicates a higher stability of the granules.

Growth media in anaerobic fermentative processes: The underestimated potential of thermophilic fermentation and anaerobic digestion

Fermentation and anaerobic digestion of organic waste and wastewater is broadly studied and applied. Despite widely available results and data for these processes, comparison of the generated results in literature is difficult. Not only due to the used variety of process conditions, but also because of the many different growth media that are used. Composition of growth media can influence biogas production (rates) and lead to process instability during anaerobic digestion. To be able to compare results of the different studies reported, and to ensure nutrient limitation is not influencing observations ascribed to process dynamics and/or reaction kinetics, a standard protocol for creating a defined growth medium for anaerobic digestion and mixed culture fermentation is proposed. This paper explains the role(s) of the different macro- and micronutrients, as well as the choices for a growth medium formulation strategy. In addition, the differences in nutrient requirements between mesophilic and thermophilic systems are discussed as well as the importance of specific trace metals regarding specific conversion routes and the possible supplementary requirement of vitamins. The paper will also give some insight into the bio-availability and toxicity of trace metals. A remarkable finding is that mesophilic and thermophilic enzymes are quite comparable at their optimum temperatures. This has consequences for the trace metal requirements of thermophiles under certain conditions. Under non-limiting conditions, the trace metal requirement of thermophilic systems is about 3 times higher than for mesophilic systems.

Aerobic Granule Reactor Technology

A new development for the treatment of domestic wastewater is a technology based on aerobic granular sludge. Granular sludge can be developed under specific process conditions. Because of the unique properties of this granular sludge, high volumetric loading rates of aeration tanks can be applied. Thanks to excellent settling properties, the separation of treated wastewater and granular sludge can take place at high hydraulic loading rates. Depending on the chosen process configuration good effluent quality can be obtained, complying with the stringent effluent requirements regarding nitrogen and phosphorus, which can be expected in the future. In this way aerobic granular sludge has the potential to contribute significantly to wastewater treatment management. This report describes the results of research carried out at the Technical University of Delft. This title belongs to Water and Wastewater Practitioner Series ISBN: 9781843390671 (Print) ISBN: 9781780402901 (eBook)

Influence of chemically enhanced primary treatment on anaerobic digestion and dewaterability of waste sludge

To lower energy consumption at a sewage treatment plant (STP), primary settling could be enhanced to direct more chemical oxygen demand (COD) to anaerobic digestion (AD) for increased biogas production and decreased aeration. Primary settling can be chemically enhanced by applying flocculation aids (FAs). FAs are refractory compounds that may affect all sludge treatment facilities. In this study the consequences are investigated of the application of FAs for chemically enhanced primary treatment (CEPT) on AD and subsequent dewatering of digested sludge in a conventional STP. It was found that FAs maintain their effect throughout all sludge processing facilities. With CEPT, more readily degradable solids were removed, resulting in a higher bio methane potential of the primary sludge. In AD, FAs lowered the viscosity; meanwhile an increased hydrolysis rate was observed. But FAs also partially irreversibly bound substrate in such way that it is not available for biological degradation anymore. In subsequent dewatering of digested sludge, a higher dry solids concentration was observed with CEPT. A computer simulation showed that in a conventional STP, CEPT would not be economically feasible. However, several benefits were discussed that can make CEPT an interesting option for future low COD/N-tolerant STPs with, for example, Anammox processes for N removal.

Pre-treatments to enhance the biodegradability of waste activated sludge: Elucidating the rate limiting step

Pre-treatments for waste activated sludge (WAS) are, in most cases, an attempt to increase the biodegradation and/or improve hydrolysis rate of WAS after anaerobic digestion. This review presents an extensive analysis of WAS pre-treatments effectiveness focusing on increasing the biodegradability. In the first part of the review, WAS is considered as a cluster of organic components: proteins, carbohydrates, humic substances and cells. Based on this breakdown into components, the effect of different pre-treatments on each component (and in combination) is described. Also, possible reasons for the contradictory results frequently found among different studies dealing with the same pre-treatment are included. In the second part, the review describes the effects on volatile solids removal by digestion after pre-treatment and on the dewaterability of the final digestate. The energy balance and potential limiting factors for each pre-treatment are also taken into account. From the published works it is concluded that some pre-treatment techniques, such as thermal hydrolysis, thermal phased anaerobic digestion and low-temperature pre-treatment are effective ways to increase energy production and to improve other sludge properties, such as dewatering. However, these techniques are very energy intensive and require a large capital outlay, so research on milder pre-treatment techniques is valuable.