Abstract
Optimization of biofilm activated sludge (BAS) process via mathematical modelling is an entangle activity since economic, environmental objective and technical decision must be considered. This paper presents a methodology to optimize the operational conditions of BAS process in four steps by combining dynamic simulation techniques with non-linear optimization methods and with operative decision-making criteria. Two set of variables are separately prioritized in the methodology: essential variables related to physical operation to enforce established process performance, and refinement variables related to biological processes that can generate risks of bulking, pin-point floc and rising sludge. The proposed optimization strategy is applied for the treatment of high COD wastewater under nutrient limitation using an integrated mathematical model for COD removal that include predation, hydrolysis and a simplified approach to the limiting solids flux theory in the secondary clarifier in order to facilitate the convergence of the optimization solver. The methodology is implemented in a full-scale wastewater treatment plant for a cellulose and viscose fibre mill obtaining (i) improvement of the effluent quality index (Kg pollution/m3) up to 62% and, (ii) decrease the operating cost index (€/m3) of the process up to 30% respect the regular working operational conditions of the plant. The proposed procedure can be also applied to other biological treatments treating high COD nutrient-limited industrial wastewater such as from textile and winery production among others.
Highlights
Emission limits for industrial effluent are constantly being tightened up
The simplified approach proposed by von Sperling (2007) takes into account four variables i) hydraulic loading rate (HLR) which corresponds to the quotient between the influent flow rate (Qi) and the surface area of the secondary settler (A), ii) solids loading rate (SLR) which corresponds to the quotient between applied solids load and the surface area of the secondary settler, iii) sludge settling velocity (v)
The operating cost index (OCI) is calculated as the weighted sum of aeration energy associated to the oxygen consumption for the carbonaceous demand (CD), aeration energy associated to the oxygen consumption for the nitrogenous demand (ND), mixing energy (ME), pumping energy (PE), sludge production (SP) and nutrient cost (NC), using the weighting factors as Chen et al 2015 and Zhou et al 2015
Summary
SNIACE, Carretera de Ganzo S/N 39300 Torrelavega Cantabria, Spain. Green Engineering & Resources Research Group (GER). Berta Galan: ORCID Code: 0000-0003-2145-3669 effluent quality, decision making
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