A cost-effective IoT strategy for remote deployment of soft sensors - a case study on implementing a soft sensor in a multistage MBBR plant.

Model-based soft sensors can enhance online monitoring in wastewater treatment processes. These soft sensor scripts are executed either locally on a programmable logic controller (PLC) or remotely on a system with data-access over the internet. This work presents a cost-effective, flexible, open source IoT solution for remote deployment of a soft sensing algorithm. The system uses low-priced hardware and open-source programming language to set up the communication and remote-access system. Advantages of the new IoT architecture are demonstrated through a case study for remote deployment of an Extended Kalman Filter (EKF) to estimate additional water quality parameters in a multistage moving bed biofilm reactor (MBBR) plant. The soft-sensor results are successfully validated against standardised laboratory measurements to prove their ability to provide real-time estimations.

Multi-parameter based coagulant dosing control.

The required coagulant dosage is strongly related to the quality of raw water or wastewater. Online sensors for most quality parameters are now readily available to treatment facilities, yet remain rarely used in treatment process control. This paper presents the evaluation of an advanced coagulant dosing control system based on online measurements in full-scale processes. The popular multivariate analytical method, partial least square regression, was used to build up the relationship between the coagulant dose and wastewater quality. The system was tested in two wastewater treatment plants (WWTPs) in Norway. Coagulant savings up to 30% in Norwegian plants were observed with feed forward calibrations. The considerable savings reduce sludge production, leading to further cost saving on sludge treatment. This paper presents the method, function and experiences of the full-scale implementation of the system in different WWTPs.

Improvement of multi-parameter-based feed-forward coagulant dosing control systems with feed-back functionalities.

Coagulant dosing control in drinking and wastewater treatment plants (WWTPs) is often limited to flow proportional concepts. The advanced multi-parameter-based dosing control systems have significantly reduced coagulant consumption and improved outlet qualities. Due to the long retention time in separation stages, these models are mostly based on feed-forward (FF) models. This paper demonstrates the improvement of such models with feed-back (FB) concepts with simplifications, making it possible to use even in systems with long separation stages. Full-scale case studies from a drinking water treatment plant and a WWTP are presented. The model qualities were improved by the dosage adjustment of the FB model, ranging from 66% to 197% of the FF model. Hence, the outlet qualities became more stable and coagulant consumption was further reduced in the range of 3.7%-15.5%.

Image analysis of sludge aggregates obtained at preliminary treatment of sewage.

The results of wastewater treatment by Al and Fe salts and by electrocoagulation with aluminum electrodes are discussed and interpreted. Those processes used alone or combined with biological treatment, were analyzed for 50 and 90% removal of phosphates. Scanning electron microscopy (SEM) of the resulting sludge from three coagulation processes defined the perimeter P and area A of 129-142 differently sized objects in each contrast-enhanced image. Plots of lg A against lg P revealed that the analyzed sludge samples were made of self-similar aggregates-flocs with fractal characteristics. The slope of 'log plots' was used to determine surface fractal dimension Da, which was extrapolated to volumetric fractal dimension Dv. Dv was applied in a quantitative description of sludge aggregates-flocs. Aggregates-flocs of sludge obtained by Al ions (pre-polymerized Al and electrocoagulation) were characterized by higher values of Dv in comparison with sludge obtained by iron salts. The structure of {Al(OH)(3)} and {Fe(OH)(3)} aggregate-flocs was graphically simulated to determine the effect of size distribution and Dv on sweep flocculation and sludge separation and dehydration. Phosphate removal efficiency of 50% occurred at low ratios of Al:P and Fe:P. Adsorption-charge neutralization was suggested during coagulation with pre-polymerized coagulants, and sweep flow mechanism during electrocoagulation.

Simulation program for wastewater coagulation.

The lack of comprehensive simulation models for wastewater coagulation is one of the obstacles to achieving optimal coagulant dosing. Two approaches for developing a model to describe the coagulation process are presented. The comprehensiveness in describing the influent quality with several parameters, rather than with one parameter, is identified to give high efficiency in dosing models based on algorithms constructed using the partial least squares method. The concept was tested on two full-scale wastewater treatment plants, with coagulant savings and effluent quality improvements. Significant differences were observed with the increase of online parameters in the models. The second approach is based on distribution of coagulant for particle and phosphate removal processes and is discussed for inert fractions. The concept is integrated into existing simulation software as a module. The calibration results and dosage predictions are demonstrated.