The present-day treatment of pulp and paper mill effluents can be significantly improved by incorporating biogas production in the context of industrial symbiosis. In this work a new industrial symbiosis concept is presented, the focus being on modelling it in view of process optimization, design improvement and adoption by the pulp and paper industry. The concept consists of a first stage in which pulp and paper mill effluents are treated by high-rate anaerobic digestion in external circulation sludge bed (ECSB) reactors to produce biogas. In the second stage the removal of organic matter contained in the anaerobic effluent stream occurs through aerobic activated sludge treatment, aiming to achieve maximum sludge production with minimum aeration requirements. This sludge should in the case study then be co-digested with residues from fish farming industry to yield methane for energy production, nutrient-rich reject water that can be recycled to the activated sludge treatment for optimum microbial activities and production of a nutrient-rich soil amendment. The overall research aim was in this project to develop a mathematical model that describes the relevant process units and the dynamics of the different processes involving organic matter removal, biogas production and nutrient release. The plant-wide model used integrated activated sludge and anaerobic models with a physico-chemical modelling framework. Through systematic calibration good general agreement was obtained between the full-scale experimental and simulated results at steady state. Acceptable differences between measured and modelled biogas production (flow rate and methane concentration), nutrients release (N and P) and effluent quality (N, P and COD) of 2-3.2 %, 5.3-7.4 % and 1.4-1.9 %, respectively, were observed throughout the full-scale system. Model-based analysis shows that the model can predict and give insight on dynamic behaviours resulting from deliberate changes but also on disturbances in one of the systems and their subsequent impacts within the integrated plant. Additionally, the model allowed the prediction of nutrients release in anaerobic digestion and subsequent consumption upstream in the high-rate anaerobic system or activated sludge system. Simulations show that there is a need for imposing a basic control and operational strategy for efficient reject water recirculation to optimize the concentrations of N and P in the activated sludge system while also achieving nutrient levels required to meet the effluent discharge permits. Overall, the evaluated plant-wide model can jointly describe the relevant physico-chemical and biological processes and is therefore advocated as a tool for future extension of this type of industrial symbiosis concepts between biogas producers and industries producing large amounts of wastewater rich in organic material. The model can be used for design, multi-criteria performance assessment and optimization of different treatment plants.

The present-day treatment of pulp and paper mill effluents can be significantly improvedby incorporating biogas production in the context of industrial symbiosis. In this work anew industrial symbiosis concept is presented, the focus being on modelling it in view ofprocess optimization, design improvement and adoption by the pulp and paper industry.The concept consists of a first stage in which pulp and paper mills effluents are treatedby high-rate anaerobic digestion in external circulation sludge bed (ECSB) reactors toproduce biogas. In the second stage the removal of organic matter contained in thedigestate stream occurs through aerobic activated sludge treatment, aiming to achievemaximum sludge production with minimum aeration requirements. This sludge shouldin the case study then be co-digested with fish-waste silage to yield methane for energyproduction, nutrients-rich reject water that can be recycled to the activated sludgetreatment for optimum microbial activities and, production of nutrient rich soilamendment. The overall research aim is to develop a mathematical model that describesthe relevant process units and the dynamics of the different processes involving organicmatter removal, biogas production and nutrients release. The review overall finds thatan integrated model is required to simulate this concept and should include recentdevelopments in activated sludge, anaerobic digestion and physico-chemical modelling.

Stringent phosphorus discharge standards (i.e. 0.15–0.3 g P.m −3 ) in the Baltic area will compel wastewater treatment practice to augment enhanced biological phosphorus removal (EBPR) with chemical precipitation using metal salts. This study examines control of iron chemical dosing for phosphorus removal under dynamic loading conditions to optimize operational aspects of a membrane biological reactor (MBR) pilot plant. An upgraded version of the Benchmark Simulation Model No. 2 (BSM2) with an improved physico-chemical framework (PCF) is used to develop a plant-wide model for the pilot plant. The PCF consists of an equilibrium approach describing ion speciation and pairing, kinetic minerals precipitation (such as hydrous ferric oxides (HFO) and FePO 4 ) as well as adsorption and co-precipitation. Model performance is assessed against data sets from the pilot plant, evaluating the capability to describe water and sludge lines across the treatment process under steady-state operation. Simulated phosphorus differed as little as 5–10% (relative) from measured phosphorus, indicating that the model was representative of reality. The study also shows that environmental factors such as pH, as well operating conditions such as Fe/P molar ratios (1, 1.5 and 2), influence the concentration of dissolved phosphate in the effluent. The time constant of simultaneous precipitation in the calibrated model, due to a step change decrease/increase in FeSO 4 dosage, was found to be roughly 5 days, indicating a slow dynamic response due to a multi-step process involving dissolution, oxidation, precipitation, aging, adsorption and co-precipitation. The persistence effect of accumulated iron-precipitates (HFO particulates) in the activated sludge seemed important for phosphorus removal, and therefore solids retention time plays a crucial role according to the model. The aerobic tank was deemed to be the most suitable dosing location for FeSO 4 addition, due to high dissolved oxygen levels and good mixing conditions. Finally, dynamic model-based analyses show the benefits of using automatic control when dosing chemicals. © 2019 Elsevier Ltd