Reducing energy costs of the wastewater treatment plant by improved scheduling of the periodic influent load

Process innovations and circular strategies for closing the water loop in a process industry

By implementing advanced wastewater treatment technologies coupled with digital tools, high-quality water is produced to be reused within the industry, enhancing process efficiency and closing loops. This paper investigates the impact of three innovation tools (process, circular and digital) in a Solvay chemical plant. Four technologies of the wastewater treatment plant "WAPEREUSE" were deployed, predicting their performance by process modelling and simulation in the PSM Tool. The environmental impact was assessed using Life Cycle Assessment and compared to the impact of the current industrial effluent discharge. The circularity level was assessed through three alternative closed-loop scenarios: (1) conventional treatment and discharge to sea (baseline), (2) conventional and advanced treatment by WAPEREUSE and discharge to sea, (3) conventional and advanced treatment by WAPEREUSE and industrial water reuse through cross-sectorial symbiotic network, where effluents are exchanged among the process industry, municipality and a water utility. Scenario 1 has the lowest pollutants' removal efficiency with environmental footprint of 0.93 mPt/m3. WAPEREUSE technologies decreased COD by 98.3%, TOC by 91.4% and nitrates by 94.5%. Scenario 2 had environmental footprint of 1.12 mPt/m3. The cross-sectorial symbiotic network on the industrial value chain resulted in higher industrial circularity and sustainability level, avoiding effluents discharge. Scenario 3 is selected as the best option with 0.72 mPt per m3, reducing the environmental footprint by 21% and 36% compared to Scenarios 1 and 2, respectively.

Plant-wide modeling of a metropolitan wastewater treatment plant to reduce energy consumption and carbon footprint

A real metropolitan wastewater treatment plant (RWWTP) serving a population equivalent of 1.55 million was modeled to reduce energy consumption and carbon footprint (CFP). An approach was proposed to handle the dilution factor and partial aeration due to discontinuous air diffuser locations in the Bardenpho-5 configuration. Various operational, structural, and configurational modifications were evaluated. Results indicated that management scenarios might provide conflicting outcomes for different targets. Reduced energy consumption may not result in lower CFP at the same time. Moreover, operational changes that would impact total nitrogen (TN) concentrations and N₂O release may significantly impact CFP. A policy of using a modified Bardenpho-5 process with reduced internal recycle (IR) ratio, waste activated sludge (WAS), and return activated sludge (RAS) flow rates provided the lowest CPF. Modified Bardenpho-5 process and replacing belt thickeners with gravity thickeners supplied the highest savings in energy consumption. Overall, up to 14% and 20% reductions were possible in the energy consumption and CFP of the plant, respectively. The RWWTP may save up to 10% in energy expenses annually by operational modifications.

Long-term nitrite-oxidizing bacteria suppression in a continuous activated sludge system exposed to frequent changes in pH and oxygen set-points

Research has proven the adaptation of nitrite-oxidizing bacteria to unfavorable environmental conditions, and this work presents a novel concept to prevent nitrite oxidation during partial nitrification in wastewater. The approach is based on the real-time updating of mathematical models of the process to search for optimal set-points of pH and oxygen concentration in a continuous activated sludge reactor with a high sludge age (20.3 days). A heuristic optimization technique by 13 optimum set-points simultaneously maximized the degree of ammonia oxidation (α) and nitrite accumulation (β), achieving an (α + β) = 190% per day. The activated sludge reactor was conducted for 780 days under three control schemes: open-loop control, fuzzy model supervisory control and phenomenological supervisory control. The phenomenological supervisory control system achieved the best results, simultaneously reaching 95% ammonium oxidation and 90% nitrite accumulation. The Haldane kinetics were analyzed using steady-state concentrations of all nitrogen species, concluding that the simultaneous maximization of α + β led to selecting set-points at the extreme values of the following ranges: pH = 7.5-8.5 and DO = 0.8-1.0 mg O₂/L, which enabled the inhibition of one nitrifier species. At the same time, the other one was relieved from inhibition. The 16sRNA assays indicated that the nitrite-oxidizing bacteria presence (genera Nitrobacter and Nitrospira) shifted from 32% to less than 8% after 280 days of continuous operation with optimal pH and oxygen set-points.

Scheduling of Batch Operation for a Wastewater Treatment Plant under Time-of-Use Electricity Pricing

High operating cost caused by electric energy consumption is a common problem challenging many municipal wastewater treatment plants (WWTPs). Due to the characteristics of intermittent inflow and aeration, WWTPs using sequencing batch reactor technology and its variants can be managed to relieve operating cost through taking advantage of time-of-use electricity pricing. However, little attention has been paid to the scheduling of treatment processes in the context of WWTPs. In this paper, a novel mixed-integer linear programming model is established for scheduling the batch operation of a WWTP under time-of-use electricity pricing, which considers constraints arising from task allocation, processing sequence, and processing duration. The modeling method is developed from the event-based continuous-time approach. The start time and end time of each treatment task are optimized to shift electricity consumption from peak hours to off-peak hours to the greatest extent, thus minimizing electricity cost. A case study demonstrates that the proposed model can quickly generate precise operational plans for the investigated WWTP. By implementing the optimum schedules, the WWTP can save on its electricity bill without changing the treatment capacity or the treatment process. The widening of peak and off-peak electricity pricing gap is favorable for the proposed model to display a more significant effect in reducing electricity cost.

Energy Consumption and Carbon Footprint of Greek Wastewater Treatment Plants

Wastewater treatment plants (WWTPs) exhibit significant energy consumption and produce large amounts of Greenhouse Gas emissions (GHG emissions). Energy efficiency and reduction in GHG emissions in WWTPs have become important issues, especially in view of the climate crisis. The core objective of this work is to assess the energy and carbon footprint of Greek WWTPs and to propose methods to improve energy efficiency and reduce GHG emissions. Data were collected from 31 Greek WWTPs with an average treatment capacity between 250 and 3,650,000 population equivalents (PE). The total population served by the 31 WWTPs was over 6,000,000, which is more than half of the population in Greece with access to WWTPs. Based on the results, the annual average energy consumption for small, medium and large WWTPs equals 137 kWh/PE, 48 kWh/PE and 32 kWh/PE, respectively. Accordingly, annual average GHG emissions, both biogenic and non-biogenic in small, medium and large WWTPs are equal to 207 kgCO2e/PE, 144 kgCO2e/PE and 89 kgCO2e/PE, respectively. Annual average on-site GHG emissions are equal to 56.5 kgCO2e/PE, while the average off-site GHG emissions account for 16.9 kgCO2e/PE. Based on the results, acceptable and attainable targets for WWTPs energy consumption and GHG emissions are proposed.

Improving stability of mainstream Anammox in an innovative two-stage process for advanced nitrogen removal from mature landfill leachate

This study presents an innovative mainstream Anammox based on multiple NO₂^--N supplement pathways to treat actual mature landfill leachate over 180 days. Desirable effluent quality of 11.8 mg/L total nitrogen (TN) and nitrogen removal efficiency of 98.8% were achieved despite fluctuation conditions of 1.5-fold influent substrates and 8.0-fold dissolved oxygen overload. Nitrogen mass balance confirmed Anammox was the dominant nitrogen removal pathway, contributing up to 87.9%. Functional genes of ammonia monooxygenase (amoA), hydrazine synthase (hzsB), and ratio of nitrate/nitrite reductase were highly detected. Anammox genera, Candidatus_Kuenenia (4.1%) and Candidatus_Brocadia (5.3%) were dominant in two functional systems, respectively, due to the different affinity of nitrite, oxygen, and organic carbon. As an economical and sustainable technology, the innovative process enabled a 95.1% decrease in organic carbon demand, a 61.5% reduction in aeration energy consumption, and 77.6% lower biomass production compared with traditional nitrification-denitrification process.

Data Driven Detection of Different Dissolved Oxygen Sensor Faults for Improving Operation of the WWTP Control System

Sensor faults frequently occur in wastewater treatment plant (WWTP) operation, leading to incomplete monitoring or poor control of the plant. Reliable operation of the WWTP considerably depends on the aeration control system, which is essentially assisted by the dissolved oxygen (DO) sensor. Results on the detection of different DO sensor faults, such as bias, drift, wrong gain, loss of accuracy, fixed value, or complete failure, were investigated based on Principal Components Analysis (PCA). The PCA was considered together with two statistical approaches, i.e., the Hotelling’s T2 and the Squared Prediction Error (SPE). Data used in the study were generated using the previously calibrated first-principle Activated Sludge Model no.1 for the Anaerobic-Anoxic-Oxic (A2O) reactors configuration. The equation-based model was complemented with control loops for DO concentration control in the aerobic reactor and nitrates concentration control in the anoxic reactor. The PCA data-driven model was successfully used for the detection of the six investigated DO sensor faults. The statistical detection approaches were compared in terms of promptness, effectiveness, and accuracy. The obtained results revealed the way faults originating from DO sensor malfunction can be detected and the efficiency of the detection approaches for the automatically controlled WWTP.

Dairy wastewater processing and automatic control for waste recovery at the municipal wastewater treatment plant based on modelling investigations

Based on the calibrated model for an Anaerobic-Anoxic-Oxic (A²O) municipal wastewater treatment plant (WWTP), this research investigated and proposed feasible solutions, control system configurations and optimal operating conditions for the dairy wastewater processing. The steady state study on adding different daily amounts of dairy wastewater in the WWTP water line revealed the most efficient amount to be treated by finding a minimum of the total nitrogen concentration in the water effluent. The dynamic investigations on adding different daily amounts of diary wastewater demonstrated the incentives of the proposed cascade control system configurations, based on the ammonia or nitrates concentration control in the aerated reactors, associated to nitrates and nitrites concentration control in the anoxic reactor. The best periods of time and duration for scheduling the dairy wastewater processing were searched and found. Preliminary results showed the incentives of the additional dairy wastewater distribution during 2 h, at the highest influent concentration moments. Further investigations, relying on the genetic algorithm optimization method revealed that better daily scheduling of the dairy wastewater addition may be obtained. Compared to normal operation, the optimal scheduling program of the dairy wastewater treatment showed an overall performance index improvement of 13.36%, when the daily 1:52 p.m. moment of time and the duration of about 1 h program, found by optimization, were applied. Results demonstrate the dual incentives of the carbon and nutrients recovery, associated to the energy and effluent quality benefits on WWTP operation.

Economic sustainability benchmarking of environmental initiatives: a case of wastewater treatment plant

Purpose

It has been long debated whether the three bottom lines of sustainability (economic, environmental and social) can be achieved simultaneously or whether achieving one adversely affects the others. This paper analyses the economic sustainability of an environmental initiative, namely, effluent treatment plant (ETP), adopted by an Indian textile industry.

Design/methodology/approach

Two situations have been considered for the analysis. First, pure economic view with the operating and installed capacities has been considered. Second, combined economic-environmental view using shadow prices of undesirable outputs (biological oxygen demand, chemical oxygen demand, total nitrogen, total phosphorous, etc.) has been analysed.

Findings

It has been found that when pure economic view is considered, the net present value (NPV) of the ETP with present operating capacity (10,200 kL/day) is negative, implying that it is not economically sustainable. However, if the ETP is operated with the full installed capacity (17,000 kL/day), it becomes economically sustainable except in the case of very high cost of capital (13%). Finally, when shadow prices of undesirable outputs are considered, the NPV becomes positive, bolstering the economic-environmental sustainability of ETP.

Research limitations/implications

In future, multiple case studies should be conducted in similar organisations to extend the general applicability of the outcome of this study. This research considers the economic and environmental aspects of ETP. However, social benefits have not been considered in this research work, which can definitely be addressed in future endeavours.

Practical implications

Though very high capital investment of ETP acts as a barrier, the results of this study imply that the top management of textile and clothing organisations should look at it from the holistic economic-environmental viewpoint. The use of ETP also leads to social benefits by improving the health of local community and by reducing their hospitalisation, medical expenditure and absenteeism from school and workplace. The outcome of this research may enthuse the entrepreneurs to adopt environmental initiatives.

Originality/value

The paper provides a framework to evaluate the economic feasibility of ETP by considering the time value of money. It is demonstrated with a real case that the environmental initiatives can be economically rewarding.

Green development challenges within the environmental management framework

Green development of energy, water and environment systems is essential as these three systems represent the basic life needs of humankind. Therefore, environmental problems arising from each of these three systems need to be carefully addressed to preserve the energy, water and environment resources for future generations. This paper discusses some of the latest developments in three main areas of sustainability themes, namely energy, water and environment, that emerged from the 14th Sustainable Development of Energy, Water and Environment Systems (SDEWES) Conference held in 2019. As such, it acts as an editorial paper for the virtual special issue of the Journal of Environmental Management, dedicated to the SDEWES 2019 conference.