Paul Lessard

Dynamic modelling of the activated sludge process: Improving prediction using neural networks

A procedure has been developed to improve the accuracy of an existing mechanistic model of the activated sludge process, previously described by Lessard and Beck [Wat. Res. 27, 963–978 (1993)]. As a first step, optimization of the numerous model parameters has been investigated using the downhill simplex method in order to minimize the sum of the squares of the errors between predicted and experimental values of appropriate variables. Optimization of various sets of parameters has shown that the accuracy of the mechanistic model, especially on the prediction of the dissolved oxygen (DO) in the mixed liquor, can be easily improved by adjusting only the values of the overall oxygen transfer coefficients, KL a. Then, in a second step, neural network models have been used successfully to predict the remaining errors of the optimized mechanistic model. The coupling of the mechanistic model with neural network models resulted in a hybrid model yielding accurate simulations of the five key variables of the activate sludge process.

Nitrogen and phosphorus removal by high latitude mat-forming cyanobacteria for potential use in tertiary wastewater treatment

As part of a program to develop biological wastewatertreatment systems for cold climate areas four strainsof filamentous, mat-forming cyanobacteria isolatedfrom Arctic and Antarctic environments were evaluatedfor their nutrient stripping and growth capabilities. A tropical strain, Phormidium bohneri, known forits excellent performance in wastewater treatment, wasused as a comparison. Experiments were done inartificial media under controlled batch cultureconditions to avoid interactions with indigenousmicroorganisms such as bacteria and protozoa. Theculture medium simulated real effluents containinghigh concentrations of nitrate and phosphate.Temperatures (5, 15 and 25°C) and irradiances(80, 210, 350, 640 and 1470 µmol photon m-2s-1) wereselected according to situations encountered in avariety of field conditions. For all irradiancelevels, growth was satisfactory at 15 and 25 °C,but limited at 5 °C. At 25 °C a satisfactory nitrogen removal rate (3.5and 4.0 mg N L-1d-1) was obtained forone polar strain (Phormidium tenue) and thecontrol P. bohneri. At 15 °C, the bestnitrogen removal rate (3.5 mg N L-1d-1)was measured with P. bohneri while the best ratefor the polar strains was around 2.3 mg NL-1d-1. At 15 °C, a phosphorusremoval rate of 0.6 mg P L-1d-1 wasobtained with P. bohneri and polar strains P. tenue and Oscillatoria O-210. Nitrogen(NO3-) and phosphorus (PO43-)uptake rates increased as a function of irradianceover the range 80 to 350 μmolphoton m-2s-1. Our results indicate thattertiary biological wastewater treatment at lowtemperatures (5 °C) cannot be anticipated withthe polar strains tested, because they arepsychrotrophic rather than psychrophilic and thus growtoo slowly under conditions of extreme cold. However, it appears that these cyanobacteria would beuseful for wastewater treatment at moderately cooltemperatures (c. 15 °C), which are commonduring spring and fall in northern climates.

Biotreatment of fish farm effluents using the cyanobacterium Phormidium bohneri

The potential environmental impact of effluent from fish farms is of increasing environmental concern. Although concentrations in total nitrogen and phosphorus are usually low, their impact on the environment cannot be ignored because of the high nutrient mass flows utilized during fish farming. In this paper we investigated the use of a non-toxic cyanobacterium, Phormidium bohneri, to remove dissolved inorganic nutrients from fish farm effluents. Wastewater was directed toward three completely mixed 70 1 photobioreactors with retention time of 8, 12 and 24 h, respectively. Average efficiencies of ammonia nitrogen removal from rainbow trout (Oncorhynchus mykiss) effluent was 82% and 85% for soluble orthophosphate, over a 1 month period. From these results, the potential use of P. bohneri as an alternative for the tertiary treatment of fish farm effluents is analyzed.

Effect of phosphorus addition on nutrient removal from wastewater with the cyanobacterium Phormidium bohneri

Abstract The growth and inorganic nutrient removal capacity of the cyanobacterium Phormidium bohneri on domestic wastewater were investigated in outdoor 24-l triangular bioreactors with or without the presence of added inorganic phosphate. While the addition of monopotassium phosphate did result in up to 56% more biomass production and had an influence on the kinetics of the removal of inorganic nutrients, it did not significantly affect the total time taken for complete removal of these nutrients. In all cases, nitrogen (ammonium and nitrate) and phosphate were removed after 50 and 75 h of growth, respectively. Biomass productivities of 23–57 mg d.m. l −1 day −1 , combined with rates of ammonium and phosphate removal up to 20 mg l −1 day −1 indicated that P. bohneri has a good potential for wastewater treatment. In the presence of added phosphate, after 40 h of growth, rates of phosphate removal became erratic, with peaks of phosphate appearing at the beginning of the daylight. These results were interpreted in relation to the complex dynamic equilibrium existing between different forms of phosphate.

Monitoring biofilter clogging: biochemical characteristics of the biomass

The low temperature of the snowmelt water in the spring seems to affect the biofiltration of wastewaters; biofilters clog rapidly during the critical period of March and April. This study presents the results of biochemical tests carried out in wash-water (biomass) of a Biodrof®-type biofilter. These tests deal with the measurement of hydrolase, dehydrogenase (DHA) and total polysaccharides (TP). The wash-water analyses showed ratios of 41% total polysaccharides over VSS (w/w) during the cold period, corresponding to influent temperatures of 7.5–13.5°C. During the warmer period (15.0–18.0°C), this ratio is 26%. Observations of the biomass show an abundance of fixed ciliated protozoans during the cold period, being replaced by a bacterial and fungal biofilm during the warmer period. Moreover, during the cold period, the biomass contains less extra-cellular enzyme like β-glucosidase type, but the ratio of active biomass measured using the dehydrogenase glucose (DHA) is the same for all temperature ranges measured here. This implies that weak hydrolytic activity, coupled with accumulation of a biofilm and inert particles of the influent encourages a rapid clogging of the biofilter. The loads in CODt and SS as well as the filtration rates have but little effect on the premature clogging of the biofilter under spring conditions.

Polar cyanobacteria versus green algae for tertiary waste-water treatment in cool climates

Forty-nine strains of filamentous, mat-forming cyanobacteria isolated from the Arctic, subarctic and Antarctic environments were screened for their potential use in outdoor waste-water treatment systems designed for cold north-temperate climates. The most promising isolate (strain E18, Phormidium sp. from a high Arctic lake) grew well at low temperatures and formed aggregates (flocs) that could be readily harvested by sedimentation. We evaluated the growth and nutrient uptake abilities of E18 relative to a community of green algae (a Chlorococcalean assemblage, denoted Vc) sampled from a tertiary treatment system in Valcartier, Canada. E18 had superior growth rates below 15°C Canada. (µ = 0.20 d-1 at 10°C under continuous irradiance of 225 µmol photon m-2 s-1) and higher phosphate uptake rates below 10°C (k = 0.050 d-1 at 5°C) relative to Vc (µ=0.087 d-1 at 10°C and k = 0.020 d-1 at 5°C, respectively). The green algal assemblage generally performed better than E18 at high temperatures (at 25°C, µ = 0.39 d-1 and k = 0.34 d-1 for Vc; µ = 0.28 d-1 and k = 0.33 d-1 for E18). However, E18 removed nitrate more efficiently than Vc at most temperatures including 25°C. Polar cyanobacteria such as strain E18 are appropriate species for waste-water treatment in cold climates during spring and autumn. Under warmer summer conditions, fast-growing green algae such as the Vc assemblage are likely to colonize and dominate, but warm-water Phormidium isolates could be used at that time.

Dynamic modelling of the activated sludge process: a case study

Abstract Description of the unsteady-state behaviour of the activated sludge process of wastewater treatment has attracted much attention, yet there have been few exhaustive assessments of the resulting models against field data from full-scale plants. This paper presents results for the evaluation of a model for carbonaceous and nitrogenous substrate removal with reference to a comprehensive set of data obtained from a 10-day monitoring exercise at the Norwich Sewage Works in eastern England. The model of the aerator is a simplified version of the IAWPRC model of the activated sludge process. The model of the secondary clarifier employs a conventional empirical expression for clarification and a conventional flux theory for thickening. Solute transport through both the aerator and clarifier is characterized by appropriate arrangements of fixed and variable-volume CSTR elements. Substrate removal and the production, thickening and recycle of biomass (suspended solids) are well replicated by the model. However, fundamental weaknesses are apparent in the currently available representations of the clarification function. Impacts of recycled flows from a sludge consolidation tank are also examined; sensitivity tests with the model suggest that these flows are a significant factor in the longer-term maintenance of aerator biomass concentration.

Data reconciliation for wastewater treatment plant simulation studies-planning for high-quality data and typical sources of errors.

Model results are only as good as the data fed as input or used for calibration. Data reconciliation for wastewater treatment modeling is a demanding task, and standardized approaches are lacking. This paper suggests a procedure to obtain high-quality data sets for model-based studies. The proposed approach starts with the collection of existing historical data, followed by the planning of additional measurements for reliability checks, a data reconciliation step, and it ends with an intensive measuring campaign. With the suggested method, it should be possible to detect, isolate, and finally identify systematic measurement errors leading to verified and qualitative data sets. To allow mass balances to be calculated or other reliability checks to be applied, few additional measurements must be introduced in addition to routine measurements. The intensive measurement campaign should be started only after all mass balances applied to the historical data are closed or the faults have been detected, isolated, and identified. In addition to the procedure itself, an overview of typical sources of errors is given.

Traitement tertiaere d'un effluent domestique secondaire par culture intensive de la cyanobactérie Phormidium bohneri

Abstract Phormidium bohneri, a self‐flocculating cyanobacterium, was grown outdoors in a 75 1 intensive culture basin (semi‐continuous system) and used for the tertiary treatment of domestic wastewater. The behavior, growth and purification potential of P. bohneri were studied. The nutrient removal efficiency (max.: Ni = 83%, 12.5 mgN 1‐1 d‐1; Pi =81%, 1.3 mg P l‐1 d‐1) of this process allows a quite rapid treatment of the secondary effluent (hydraulic retention time=1d). Stripping account for about 62% of nitrogen (NH3) removal while 38% is assimilated by P. bohneri. Inorganic phosphorus is removed mainly by precipitation (57%) and to a lesser extent is taken‐up by Phormidium (43%). The cyanobacterial biomass (P: 1.1%, N: 8.6%, protein: 53.5%, dry weight basis) can be easily harvested after the treatment by settling.

Nitrogen elimination mechanisms in an organic media aerated biofilter treating pig manure

Biofilters using organic media are known to procure efficient treatment for different types of wastewater, but the nitrogen removal pathways implied are still not well understood. In this study, a lab-scale aerated biofilter using peat and treating pig manure was operated for 180 days, in order to quantify the nitrogen transformations occurring in it. It was shown that stripping was important during the start-up, until nitrification took place. Simultaneous nitrification and denitrification, proved by N2 production, became the principal mechanism after some time. The production of N2O did not seem to come only from heterotrophic denitrification, but also from chemodenitrification and autotrophic denitrification. It has also been found that part of the influent nitrogen was retained in the system during the first 150 days, due to filtration, sorption and assimilation. During the last periods of operation, the nitrogen previously retained has been used by microorganisms, leading to an excessive N2 discharge.