Harsha Ratnaweera

Comparison of the coagulation behavior of different Norwegian aquatic NOM sources

Abstract The coagulation behavior of eight natural water samples containing natural organic matter (NOM) was investigated to identify parameters influencing the process. The coagulation of original water samples is discussed using colour and colloidal charge composition in various molecular weight fractions. Over 40% of colours are given by NOM fractions with molecular weight cut-off (MWCO) 50 kD for all waters. The optimum coagulant dosage and the colloidal charge were shown to be proportional to the initial colour. This is also valid for dissolved organic carbon (DOC) and for UV-absorbency, which had correlations with colour of R 2 = 0.92 and 0.94, respectively. Larger NOM molecules required fewer amounts of coagulants per removed colour unit compared with smaller NOM molecules. However, it was not possible to show that the NOM molecule size influences the colloidal charge per colour unit. Zeta potentials at optimum coagulant dosages deviate from zero, indicating the presence of other coagulation mechanisms than charge neutralisation. Thus, it is difficult to use zeta potential as the only tool for online dosing coagulant control strategies.

Coagulation with Prepolymerized Metal Salts

It has been known to mankind for 4000 years that alum and iron are useful in the treatment of water. Purified alum was, however, first manufactured in the fifteenth century. In England, treatment of muddy waters by coagulation/flocculation started in the mid-seventeenth century. Today alum (or iron) coagulation represents probably the most commonly used drinking water treatment process throughout the world.

Feed supplement recovered from dairy wastewater by biological and chemical pretreatment

A continuous process for treatment of dairy wastewater with immobilized lactic acid bacteria has been demonstrated at pilot scale. A strain of Lactobacillus plantarum was selected on the basis of a high conversion rate of lactose at low pH, a high affinity of lactose at low concentrations, and the ability to retain activity for a long time immobilized in alginate beads. Lactose was converted to lactic acid, which lowered the pH and precipitated milk proteins. The proteins were separated together with milk fat by flotation with carboxy methyl cellulose (CMC) or chitosan and gave a solid phase of approx. 10% dry matter (23% protein and 68% fat). The total chemical oxygen demand (CODt) removed varied from 65 to 78% for CMC and 49 to 82% for chitosan. The precipitated material was used as a feed supplement for pigs to provide up to 30% of the total energy intake. No adverse effects on the pigs performance were observed. The energy feed value of the precipitate was estimated to be 2·0 feed units (FUs) per kg dry matter.

Climate change impacts on activated sludge wastewater treatment: a case study from Norway

We present an investigation on climate change effects on a wastewater treatment system that receive sewage collected in a combined sewer system in Oslo, Norway, during winter operation. Results obtained, by contrasting meteorological data with sewage data, show that wastewater treatment plant (WWTP) influent flow rates are significantly increased during temporary snow melting periods above a critical daily air mean temperature of approx. -1.5 degrees C degree (T(Crit)) identified in the area. In order to assess melting patterns, the number of days above and below T(Crit) was assessed, and the annual number of melting periods was additionally evaluated using meteorological data obtained in the last decade. A striking thing about the daily air temperature pattern is that, despite the progressively warmer winter temperatures in the last decade, an increasing number of days with temperatures below -1.5 degrees C could be observed. The frequency of melting periods is shown to increase in wintertime, and it is identified as an additional climate change related factor in the Oslo region. We demonstrate that these impacts can deteriorate the WWTP operation through progressively increasing the relative frequencies of very high influent flow rate and of the very low influent sewage temperature. Such climate change related effects on sewage treatment processes can be characterised as shock-conditions, i.e. significant changes in a systems boundary conditions, occurring in a relatively short period of time. In the six year period examined, biological nitrogen removal and secondary clarification processes are shown to be significantly affected by the climate factors. A striking thing about using the state-of-the-art mathematical models of wastewater treatment processes in decision support systems is their inability of describing, and thus predicting the effects of such shock-loading events, as they have not been studied so far. Adaptation and optimisation of process models, also for use in design, optimisation as well as in real-time automation and process control schemes, are thus critical to meet the challenges of climatic changes in the future.

Particle and Phosphate Removal Mechanisms with Prepolymerized Coagulants

The efficiency of wastewater treatment by chemical coagulation depends on the efficiency of each stage: (1) coagulation/precipitation, (2) flocculation, and (3) separation. The efficiency of the coagulation/precipitation stage depends on many parameters including the raw water quality, the chemistry of the coagulant, physical parameters of the process, and the expected quality of the treated water according to the needs. An adequate understanding of the mechanisms of the coagulation/precipitation process is, therefore, essential for increasing its efficiency.

Statistical monitoring and dynamic simulation of a wastewater treatment plant: A combined approach to achieve model predictive control

The on-line monitoring of Chemical oxygen demand (COD) and total phosphorus (TP) restrains wastewater treatment plants to achieve better control of aeration and chemical dosing. In this study, we applied principal components analysis (PCA) to find out significant variables for COD and TP prediction. Multiple regression method applied the variables suggested by PCA to predict influent COD and TP. Moreover, a model of full-scale wastewater treatment plant with moving bed bioreactor (MBBR) and ballasted separation process was developed to simulate the performance of wastewater treatment. The predicted COD and TP data by multiple regression served as model input for dynamic simulation. Besides, the wastewater characteristic of the wastewater treatment plant and MBBR model parameters were given for model calibration. As a result, R2 of predicted COD and TP versus measured data are 81.6% and 77.2%, respectively. The model output in terms of sludge production and effluent COD based on predicted input data fitted measured data well, which provides possibility to enabled model predictive control of aeration and coagulant dosing in practice. This study provide a feasible and economical approach to overcome monitoring and modelling restrictions that limits model predictive control of wastewater treatment plant.

An Analysis of Floc Separation Characteristics in Chemical Wastewater Treatment

Chemical treatment of wastewater consists of three unit processes: coagulation/precipitation, flocculation and floc separation, the latter normally being carried out by sedimentation. The reaction step (coagulation/precipitation) is obviously of fundamental importance to the total treatment result, but the separation steps (flocculation and floc separation) have far greater importance from an economic point of view, since separation normally takes hours to complete while the reaction is completed within seconds.

Simultaneous Phosphate Precipitation and Particle Destabilization Using Aluminium Coagulants of Different Basicity

Chemical treatment of wastewater was investigated by conducting jar tests with a synthetic testwater. The influence of different variables (pH, ortho-P concentration, particle concentration, hardness, humus concentration) on the competitive reactions of aluminium coagulants with ortho-P and hydroxyl ions, respectively, was studied under controlled conditions. The data were evaluated by assuming that basic aluminium phosphate A11.4PO4(OH)1.2, referred to as Alp and A1(0H)3 are precipitated simultaneously. The ratio A1P/A1T was found to depend on initial pH, initial ortho-P concentration, initial particle concentration and the coagulant’s basicity. In a soft water matrix, the amount of coagulant not consumed by P-precipitation was about as efficient for particle destabilization as an equal amount in the same, but ortho-P free, raw water. In hard water matrices, however, P-precipitation was found to enhance particle destabilization. Co-precipitation of calcium even at pH = 6 was identified as the main reason for this effect. Humus concentrations on the order of 5–10 mg/l can considerably increase the coagulant demand for particle destabilization. A procedure for advanced characterization and evaluation of wastewater with respect to chemical treatment is suggested.

Dairy Wastewater Treatment by Coagulation with Chitosan

The pre-treatment of dairy wastewater is important as it reduces the load to small municipal wastewater treatment plants and is attractive as it produces sludge valuable as a food additive. Only non-toxic organic polymers of biological origin are suitable for this purpose. Anionic polymers such as sodium carboxymethyl cellulose (CMC) are commonly used for treating dairy wastewater, after the pH is adjusted to 4.2–4.5, however, this process consumes both acid and base while the process stability is highly dependent on the pH. In this study, a novel coagulant, chitosan, was tested in dairy wastewater. Chitosan is made from shrimp- and crab-shell waste and is a non-toxic cationic polymer. The results indicate very good performance even at pH = 5.5. The zeta potential studies on chitosan coagulation reveals the possibility for specific chemical adsorption of the polymer. The zeta potential at which coagulation occurs seems not to be constant for a given wastewater type and coagulant, thus it is not possible to use it as a “set-point” for coagulant dosing unless combined with other parameters.

Feed-forward-based software sensor for outlet turbidity of coagulation process considering plug flow condition

Physical online sensors are widely used in wastewater treatment plants. The high costs of acquisition and maintenance as well as the delayed response due to long hydraulic retention times, applications of some physical online sensors are limited. Consequently, studies on developing software sensors have been drawn much attentions these years. Aiming to predict treatment results after water is coagulated, and this paper focuses on developing a software sensor of outlet turbidity for coagulation process. Solution to address the potential non-plug flow conditions in sedimentation tanks is discussed. Model validation results show that the proposed software sensor has 86% of accuracy within the main working range. This paper expresses a novel concept that what the proposed software sensor predicted has been not formed in the coagulation process. Since the software sensor enables to know the treatment results without waiting for long hydraulic retention time of sedimentation tank, it not only shortens the response time of manual dosing control but also serves as a feedback parameter to define optimal dosage for coagulant dosing control systems.