Glen T. Daigger

A New Planning and Design Paradigm to Achieve Sustainable Resource Recovery from Wastewater

To employ technologies that sustainably harvest resources from wastewater (for example struvite granules shown here), new perceptions and infrastructure planning and design processes are required.

The dynamics of microbial growth on soluble substrates: A unifying theory

Abstract This paper reviews the literature relevant to the dynamics of microbial growth on soluble substrates and integrates the knowledge obtained into a unifying theory describing that growth. In the unifying theory cellular mass is divided into five constituents: a synthetic component, a structural component, precursor molecules for those components, enzymes catalyzing the synthesis of the precursors, and storage products. Reactions governing the levels of those constituents are hypothesized. The literature shows that the transient response of a culture is generally either a storage response or a growth response and that environmental factors govern which response is manifested. The unifying theory is developed in a way which allows it to be simplified to either of those responses by proper selection of the rate constants in the reactions governing the levels of the cellular constituents.

Characterization of the denitrifying fraction of phosphate accumulating organisms in biological phosphate removal

Results of experimental investigations are presented that strongly support the hypothesis that PAO from activated sludge systems consist of two groups: a) denitrifying PAO (DNPAO) capable of using oxygen and nitrate and b) non-denitrifying PAO (non-DNPAO) only able to use oxygen. Batch experiments were performed in which activated sludge obtained from a pilot scale BiodeniphoTM was submitted to a sequence of anaerobic/anoxic/aerobic, anaerobic/aerobic or anaerobic/anoxic conditions while monitoring the course of NOx-N, NH4-N, PO4-P, PHB and PHV. Several methods for the determination of the two fractions of PAO are performed and compared. This study extends on previously reported results (Kern-Jespersen and Henze, 1993) in that the pH was controlled to around pH 7 to assure that phosphate precipitation was minimal, and in the measurement of PHB and PHV. With regards to the latter, the paper also examines the influence of the size of the internal PHA pool on the anoxic phosphorus uptake rate. Simulations implementing existing models for the growth of non-DNPAO and DNPAO are used to confirm the experimental results and to gain a better understanding of some of the observations.

Phosphorus Recovery Technology Modeling and Feasibility Evaluation for Municipal Wastewater Treatment Plants

A computer model was used to evaluate the economic viability of implementing phosphorus recovery processes in municipal wastewater treatment applications. The model examines investment costs, sludge volumes, sludge disposal costs, chemical costs, and the value of recovered phosphates. The model specifically focused on: 1) representative phosphorus recovery technologies integrated with representative treatment scenarios for enhanced biological nutrient removal (EBNR) with a sidestream Crystalactor® application and for conventional biological treatment followed by mainstream (tertiary) Crystalactor application; 2) the value of recovered phosphorus, assuming recovery as calcium phosphate, with a similar value to that of phosphate ore (handling and transport costs are ignored); and 3) the impacts of phosphorus recovery on major operating costs. The model results show that phosphorus recovery is most cost-effective for high phosphorus and low biochemical oxygen demand (BOD) concentration wastewaters where slud...

A model for the bio-oxidation process based on product formation concepts

Abstract Data from the literature suggests that the concentration of organic matter in the effluent from a biological reactor is influenced by the concentration in the influent. Based upon the fact that the majority of the soluble organic matter in the effluent is not the original substrate, the hypothesis is put forth that most of it is microbial in origin, and therefore consists of the products of microbiol metabolism. Using the concept that the activated sludge process is a producer of organic compounds, as well as a user of them, a model is then developed which relates the effluent COD to product formation. Previously published data is then used to establish that the specific rate of product formation is related to the specific growth rate by at least a 2nd order polynomial function. The function is given and its implication to plant design and operation are discussed.

Wastewater solids fermentation for volatile acid production and enhanced biological phosphorus removal

Fermentation of wastewater solids for volatile acid (VA) production was studied as part of a full-scale demonstration of the Orange County Water and Sewer Authority (OWASA) process for enhanced biological phosphorus removal (EBPR). The VA yields in bench-scale fermentation tests ranged between approximately 6% and 26% of feed volatile solids (VS) under a range of test conditions that included solids retention times (SRTs) between 2 and 6 days, fermenter solids concentrations between 0.43% and 2.6%, and temperatures between 14 o C and 23 o C. Higher VA yields were observed at higher SRTs, lower fermenter solids concentrations, and higher temperatures. Settleability tests indicated that gravity separation of fermented sludge may be limited to an underflow concentration of 3%. After blending a phosphorus-rich waste activated sludge (WAS) with fermented primary solids, up to 42% of the WAS phosphorus was released within 5 hours. Two full-scale demonstration fermentation designs were investigated during the study that included a 2-month simultaneous testing period. Demonstration Fermenter No. 1 used rectangular dissolved air flotation thickeners that were retrofitted with submersible mixers, liquid-solids separation zones, and covers for odor control. This unit proved difficult to operate and maintain because of the design of the unit and the demanding duty. During the 2-month side-by-side test period, the VA yield averaged 0.05 mg/mg VS fed to the unit. The average VA composition of the fermenter product stream consisted of 41 no acetic acid, 44% propionic acid, 9% butyric acid, and 5% valeric acid. Suspended solid, organic, and nutrient loads in the fermenter product stream averaged 3.1 mg solids/mg VA, 1.7 mg carbonaceous biochemical oxygen demand (CBOD 5 )/mg VA, 0.04 mg ammonia/mg VA, and 0.05 mg phosphorus/mg VA during the 8-month testing period. The second fermenter used an existing sludge-holding tank mixed intermittently with coarse bubble aeration and dewatering centrifuges for liquid-solids separation. Demonstration Fermenter No. 2 proved to be quite reliable, although it provided less discretionary control over the fermentation process compared with Fermenter No. 1. During the side-by-side test, the VA yield averaged 0.05 mg/mg VS fed to the unit. The VA composition of the fermenter product stream averaged 38% acetic acid, 36% propionic acid, 16% butyric acid, and 10% valeric acid. During the 10-month testing period, the solid, organic, and nutrient loads averaged 1.0 mg solids/mg VA, 2.4 mg CBOD 5 /mg VA, 0.15 mg ammonia/mg VA, and 0.11 mg phosphorus/mg VA in the fermenter product stream. Both demonstration fermenters produced an acceptable quality VA source for use in a 22 000 M 3 /day (6 mgd) full-scale demonstration of the OWASA EBPR process. Performance of bench-scale and full-scale demonstration fermenters was highly variable (0.05 to 0.2 mg VA/mg VS feed). Commercial acetic acid was also used as the sole volatile acid source and as a supplement to the VA stream produced from the demonstration fermenters to stabilize EBPR performance

Significance of design and operational variables in chemical phosphorus removal.

Batch and continuous experiments using model and real wastewaters were conducted to investigate the effect of metal salt (ferric and alum) addition in wastewater treatment and the corresponding phosphate removal from a design and operational perspective. Key factors expected to influence the phosphorus removal efficiency, such as pH, alkalinity, metal dose, metal type, initial and residual phosphate concentration, mixing, reaction time, age of flocs, and organic content of wastewater, were investigated. The lowest achievable concentration of orthophosphate under optimal conditions (0.01 to 0.05 mg/L) was similar for both aluminum and iron salts, with a broad optimum pH range of 5.0 to 7.0. Thus, in the typical operating range of wastewater treatment plants, pH is not a sensitive indicator of phosphorus removal efficiency. The most significant effect for engineering practice, apart from the metal dose, is that of mixing intensity and slow kinetic removal of phosphorus in contact with the chemical sludge formed. Experiments show that significant savings in chemical cost could be achieved by vigorously mixing the added chemical at the point of dosage and, if conditions allow, providing a longer contact time between the metal hydroxide flocs and the phosphate content of the wastewater. These conditions promoted the achievement of less than 0.1 mg/L residual orthophosphate content, even at lower metal-to-phosphorus molar ratios. These observations are consistent with the surface complexation model presented in a companion paper (Smith et al., 2008).

Tools for water quality monitoring and mapping using paper-based sensors and cell phones

In this paper we describe a combination of paper-based sensors and a novel smart-phone application for on-site quantification of colorimetric readouts as an ultra-low cost solution to monitoring water quality. The system utilizes a paper-based analytical device (μPAD) that produces a colorimetric signal that is dependent on the concentration of a specific target; a cell phone equipped with a camera for capturing images of two μPADs - one tested with a water sample and the other tested with clean water that is used as a control; and an on-site image processing app that uses a novel algorithm for quantifying color intensity and relating this to contaminant concentration. The cell phone app utilizes a pixel counting algorithm that performs with less bias and user subjectivity than the typically used lab-based software, ImageJ. The use of a test and control strip reduces bias from variations in ambient lighting, making it possible to acquire and process images on-site. The cell phone is also able to GPS tag the location of the test, and transmit results to a newly developed website, WaterMap.ca, that displays the quantitative results from the water samples on a map. We demonstrate our approach using a previously developed μPAD that detects the presence of organophosphate pesticides based on the inhibition of immobilized acetylcholinesterase by these contaminants. The objective of this paper is to highlight the importance and potential of developing and integrated monitoring system consisting of μPADs, cell-phones and a centralized web portal for low-cost monitoring environmental contaminants at a large-scale.

Comparison and evaluation of empirical zone settling velocity parameters based on sludge volume index using a unified settling characteristics database

Over the past few decades classic and contemporary research on the process of secondary clarification in activated sludge plants has illuminated several aspects of the solids-flux theory which actually require a closer examination. Inter alia the most challenging and controversial part in the field has been the development of reliable models for the settling properties of the activated sludge in the settler. Numerous studies have been performed aiming at the evolvement of reliable mathematical formulas that would satisfactorily describe this behaviour, but no universally accepted solution seems to exist to date. That is mostly because different experimental conditions, sludge types and instrumentation have been employed, thus complicating the process of reaching a conclusive result. In order to bring theoretical and practical developments of secondary settling tank design and simulation closer together, a number of related tasks are addressed in this study by the use of an integrated and unified settling characteristics database. Several drawbacks and advantages of the methodologies published hitherto are examined on a universal basis and under the same assumptions in order to reveal artifacts that complicate the procedure of settling velocity estimation. It is suggested that universally accepted solutions may be feasible especially for design purposes. For simulation analysis real-time data of settling velocity should be tested rather than values derived from laboratory experiments which are shown to produce different results depending on the applied approach. In conclusion, an integrated database is proposed as a means for a more robust and universally accepted design procedure.

Phosphate complexation model and its implications for chemical phosphorus removal.

Research was undertaken to analyze and verify a model that can be applied to activated sludge, integrated fixed-film activated sludge (IFAS), and moving-bed biofilm reactor (MBBR) systems. The model embeds a biofilm model into a multicell activated sludge model. The advantage of such a model is that it eliminates the need to run separate computations for a plant being retrofitted from activated sludge to IFAS or MBBR. The biofilm flux rates for organics, nutrients, and biomass can be computed by two methods-a semi-empirical model of the biofilm that is relatively simpler, or a diffusional model of the biofilm that is computationally intensive. Biofilm support media can be incorporated to the anoxic and aerobic cells, but not the anaerobic cells. The model can be run for steady-state and dynamic simulations. The model was able to predict the changes in nitrification and denitrification at both pilot- and full-scale facilities. The semi-empirical and diffusional models of the biofilm were both used to evaluate the biofilm flux rates for media at different locations. The biofilm diffusional model was used to compute the biofilm thickness and growth, substrate concentrations, volatile suspended solids (VSS) concentration, and fraction of nitrifiers in each layer inside the biofilm. Following calibration, both models provided similar effluent results for reactor mixed liquor VSS and mixed liquor suspended solids and for the effluent organics, nitrogen forms, and phosphorus concentrations. While the semi-empirical model was quicker to run, the diffusional model provided additional information on biofilm thickness, quantity of growth in the biofilm, and substrate profiles inside the biofilm.