Energy Consumption Of Wastewater Treatment Research Articles

Research on Optimization of Total Nitrogen Peak Suppression in Wastewater Treatment Based on the Data Driven Method

In order to solve the problems of water eutrophication, algae anoxic decay, and death by biological poisoning, which are caused by the excessive emission of total nitrogen in wastewater treatment process, this paper proposes a method of total nitrogen peak suppression which is based on neural network decision optimization. First, the SSORBF neural network is established according to the wastewater treatment process, and total nitrogen, inflow flow, current total nitrogen, dissolved oxygen concentration, and nitrate nitrogen concentration are selected to predict the total nitrogen concentration. Second, the density- and memory-based NSGA2 multiobjective optimization method is used to set the optimal solution to meet the requirement of energy consumption. If the prediction of total nitrogen exceeded the set value, the optimal control strategy is adopted to control the peak value of total nitrogen in advance, and it cannot exceed the national maximum allowable emission value. If the prediction of total nitrogen is lower than the set value, it continues to track the parameter set value. Finally, compared with other methods, the proposed method can effectively suppress the peak value of total nitrogen under 18 mg/L and reduce the energy consumption in wastewater treatment by 7.6%. It can provide decisions and advice for wastewater treatment plants.

Challenges of suppressing nitrite-oxidizing bacteria in membrane aerated biofilm reactors by low dissolved oxygen control

Membrane aerated biofilm reactor (MABR) and shortcut nitrogen removal are two types of solutions to reduce energy consumption in wastewater treatment, with the former improving the aeration efficiency and the latter reducing the oxygen demand. However, integrating these two solutions, i.e., achieving shortcut nitrogen removal in MABR, is challenging due to the difficulty in suppressing nitrite-oxidizing bacteria (NOB). In this study, four MABRs were established to demonstrate the feasibility of initiating, maintaining, and restoring NOB suppression using low dissolved oxygen (DO) control, in the presence and absence of anammox bacteria, respectively. Long-term results revealed that the strict low DO (< 0.1 mg/L) in MABR could initiate and maintain stable NOB suppression for more than five months with nitrite accumulation ratio above 90 %, but it was unable to re-suppress NOB once they prevailed. Moreover, the presence of anammox bacteria increased the threshold of DO level to maintain NOB suppression in MABRs, but it was still incapable to restore the deteriorated NOB suppression in conjunction with low DO control. Mathematical modelling confirmed the experimental results and further explored the differences of NOB suppression in conventional biofilms and MABR biofilms. Simulation results showed that it is more challenging to maintain stable NOB suppression in MABRs compared to conventional biofilms, regardless of biofilm thickness or influent nitrogen concentration. Kinetic mechanisms for NOB suppression in different types of biofilms were proposed, suggesting that it is difficult to wash out NOB developed in the innermost layer of MABR biofilms because of the high oxygen level and low sludge wasting rate. In summary, this study systematically demonstrated the challenges of NOB suppression in MABRs through both experiments and mathematical modelling. These findings provide valuable insights into the applications of MABRs and call for more studies in developing effective strategies to achieve stable shortcut nitrogen removal in this energy-efficient configuration.

Spatial and Temporal Modeling on Energy Consumption of Wastewater Treatment Based on Machine Learning Algorithms

Spatial and Temporal Modeling on Energy Consumption of Wastewater Treatment Based on Machine Learning Algorithms

Optimal control of sewage treatment process using a dynamic multi-objective particle swarm optimization based on crowding distance

A variety of multi-objective optimization algorithms has been extensively investigated in the past decades to tackle the optimal decision of sewage treatment process. However, achieving the ideal solutions is challenging in the multi-criteria decision-making process from Pareto optimal sets due to the complicated relationships among influencing factors, especially in the case of large decision variables involved in the wastewater treatment process. We thus proposed an improved dynamic multi-objective particle swarm optimization algorithm based on crowding distance (DMOPSO-CD) to obtain global optimal solutions for the balance between energy consumption (EC) and effluent quality (EQ) in sewage treatment processes. The algorithm consists of optimization modules and a self-organizing fuzzy neural network, improving the global searching ability of particles, maintaining the diversity of non-inferior solutions, and solving the multi-objective vital issues in the optimization of sewage treatment process. The proposed optimization algorithm was applied to benchmark simulation model No.1, and the optimization results showed that the EC for wastewater treatment in dry, rainy, and storm weather was reduced by 7.87%, 6.28%, and 7.30%, respectively. This methodology outperformed several widely applied algorithms, including the multi-objective cuckoo search, non-dominated sorting genetic algorithm-II, and improving Pareto evolutionary algorithm in terms of EQ and EC, which opens a new window for the optimal decision of sewage treatment.

Comparative assessment of energy generation from ammonia oxidation by different functional bacterial communities

Bioelectrochemical ammonia oxidation (BEAO) in a microbial fuel cell (MFC) is a recently discovered process that has the potential to reduce energy consumption in wastewater treatment. However, level of energy and limiting factors of this process in different microbial groups are not fully understood. This study comparatively investigated the BEAO in wastewater treatment by MFCs enriched with different functional groups of bacteria (confirmed by 16S rRNA gene sequencing): electroactive bacteria (EAB), ammonia oxidizing bacteria (AOB), and anammox bacteria (AnAOB). Ammonia oxidation rates of 0.066, 0.083 and 0.082 g NH4+-N L−1 d−1 were achieved by biofilms enriched with EAB, AOB, and AnAOB, respectively. With influent 444 ± 65 mg NH4+-N d−1, nitrite accumulation between 84 and 105 mg N d−1 was observed independently of the biofilm type. The AnAOB-enriched biofilm released electrons at higher potential energy levels (anode potential of 0.253 V vs. SHE) but had high internal resistance (Rint) of 299 Ω, which limits its power density (0.2 W m−3). For AnAOB enriched biofilm, accumulation of nitrite was a limiting factor for power output by allowing conventional anammox activity without current generation. AOB enriched biofilm had Rint of 18 ± 1 Ω and yielded power density of up to 1.4 W m−3. The activity of the AOB-enriched biofilm was not dependent on the accumulation of dissolved oxygen and achieved 1.5 fold higher coulombic efficiency when sulfate was not available. The EAB-enriched biofilm adapted to oxidize ammonia without organic carbon, with Rint of 19 ± 1 Ω and achieved the highest power density of 11 W m−3. Based on lab-scale experiments (scaling-up factors not considered) energy savings of up to 7 % (AnAOB), 44 % (AOB) and 475 % (EAB) (positive energy balance), compared to conventional nitrification, are projected from the applications of BEAO in wastewater treatment plants.

Insight into Greenhouse Gases Emissions and Energy Consumption of Different Full-Scale Wastewater Treatment Plants via ECAM Tool.

Greenhouse gas (GHG) production is one of the urgent problems to be solved in the wastewater treatment industry in the context of “carbon neutrality”. In this study, the carbon emissions and energy consumption of typical wastewater treatment processes in China were evaluated, starting from different cities and water treatment plants. Tool of Energy Performance and Carbon Emission Assessment and Monitoring (ECAM) was used. By comparing the influent BOD5, it was found that the energy consumption for wastewater treatment was positively correlated with the influent organic load. The annual CH4 emission of Xi’an WWTP can reach 19,215 t CO2eq. Moreover, GHGs are closely related to the wastewater treatment process chosen. WWTP B of Kunming used only an anaerobic process without continuous aeration, with an average monthly energy consumption of 8.63 × 105 kW·h. The proportion of recoverable biogas was about 90% in the GHG discharged by the traditional process. However, the anaerobic digestion-thermoelectric cogeneration process can make the recovery of the biogas utilization ratio reach 100%. Compared to the Shuozhou WWTP and WWTP A of Kunming, the Strass WWTP served the smallest population and had the largest treatment capacity, reaching the lowest energy consumption, consuming only 23,670 kW·h per month. The evaluation and analysis of ECAM provide data support and research foundation for the wastewater treatment plants to improve energy utilization and reduce greenhouse gas emissions.

Predicting sludge generation patterns and carbon reduction potential under Shared Socioeconomic Pathways

Sludge management accounts for a large share of economic costs and energy consumption in wastewater treatment and has become an important challenge for urban sustainability. Accurately predicting regional sludge generation by incorporating spatial characteristics to find carbon reduction potential can help improve the sustainability of wastewater treatment and formulate tailored mitigation strategies. This is especially true in China, which along with the world's largest wastewater treatment capacity, also faces rapid growth in sludge generation, insufficient disposal capacity, and low recycling rates. In this study, data from 3,495 wastewater treatment plants were used to screen sludge driving factors in 338 Chinese cities, and a random forest regression model was used to predict future sludge generation and associated carbon emissions at the provincial level under Shared Socioeconomic Pathways. The results showed that GDP, built-up area, and carbon content of foods had relatively high q-values (above 0.5). Indicating that economic development, urban form, and food consumption were the major factors influencing sludge generation. By 2060, total sludge generation in China is expected to be between 195% and 241% of the 2017 total in the five SSP scenarios. Improved disposal methods should be implemented to reduce carbon emissions in regions that have stable sludge growth, while fast-developing areas should focus on sludge reduction. In Central and Western China, it may be possible to control sludge generation at the source given expected changes in dietary structure and urban compact development change, while in Eastern China greater use of anaerobic digestion and sludge-to-resource treatment may be more effective. Combining anaerobic digestion and low carbon disposal methods could reduce about 50 Mts GHG emissions in China by 2060.

Decolorization of industrial wastewater using electrochemical peroxidation process

In this study, decolorization of wastewater samples taken from the paper industry is investigated using electrochemical peroxidation process. The electrochemical peroxidation process is a part of electrochemical advanced oxidation processes, which is based on the Fenton’s chemical reaction, provided by addition of external H2O2 into reaction cell. In this study, iron is used as anode and graphite as cathode put at the fixed distance of 30 mm in a glass reaction cell. The cell was filled with the solution containing wastewater and sodium chloride as the supporting electrolyte. Factors of the process such as pH, current intensity, hydrogen peroxide concentration, and time of treatment were studied. The results illustrate that all these parameters affect efficiencies of dye removal and chemical oxygen demand (COD) reducing. The maximal removal of wastewater contaminants was achieved under acid (pH 3) condition, with the applied current of 1 A, and hydrogen peroxide concentration of 0.033 M. At these conditions, decolorization process efficiency reached 100 and 83 % of COD removal after 40 minutes of wastewater sample treatment. In addition, the electrical energy consumption for wastewater treatment by electrochemical peroxidation is calculated, showing increase as the current intensity of treatment process was increased. The obtained results suggest that electrochemical peroxidation process can be used for removing dye compounds and chemical oxygen demand (COD) from industrial wastewaters with high removal efficiency.

Heavy metal ions and particulate pollutants can be effectively removed by a gravity-driven ceramic foam filter optimized by carbon nanotube implantation

It is of great significance to develop a new gravity-driven filter to remove water pollutants, but it is still challenging. Here, a novel and simple strategy is demonstrated to manufacture fly ash (FA) ceramic foams showing a three-dimensional interconnected porous structure, with multiwalled carbon nanotubes (MWCNTs) implanted by combining carbamate grafting and polydimethylsiloxane coating. The polydimethylsiloxane formed a physical coating on the carbamate group, generating an effective thermal insulating layer on the outer side of the entire MWCNT. The FA foam, which shows a sufficient adsorption capacity for Pb(II) (51.67 ± 1.17 mg g−1) and Cd(II) (30.12 ± 0.37 mg g−1) at pH = 5, T = 25 °C, has a 96.33%, 95.12%, 89.50% removal efficiency for Cd(II), Pb(II), and particulate pollutants, and exhibits excellent recycling performance. This paper provides new opportunities to fabricate gravity-driven filters with low energy consumption for wastewater treatment.

Sulfate reduction and elemental sulfur recovery using photoelectric microbial electrolysis cell

Elemental sulfur recover from sulfate-rich environment has great significance for the sustainable development of environment and energy. This study aimed to realize simultaneous sulfate reduction and elemental sulfur recovery using a novel photoelectricity microbial electrolysis cell (PMEC) under low applied voltages. At an applied voltage of 1.2 V, the sulfate reduction rate in the PMEC reached 200 ± 2.3 mg L−1 d−1, and 46.3 ± 7.9% of the reduced sulfate converted to elemental sulfur. With increasing voltages from 0.8 to 1.5 V, the sulfate reduction rates enhanced from 37.8 ± 12.4 to 236 ± 18.1 mg L−1 d−1. The recovery efficiency of elemental sulfur from removed sulfate decreased to 35% at 1.5 V, which was attributed to the higher concentration of dissolved oxygen diffusing from the anode side. Sulfate reducing bacteria (including Desulfovibrio and Desulfomicrobium) cooperated with sulfur oxidizing bacteria (including Thiomonas and Acinetobacter) for recovering elemental sulfur that could be regulated by cathode configuration. The study provided an alternative to apply solar energy in biological sulfur recovery and reduce energy consumption of wastewater treatment.

Kinetic study and performance evaluation of an integrated two-phase fixed-film baffled bioreactor for bioenergy recovery from wastewater and bio-wasted sludge

The present study evaluated the performance of an integrated two-phase fixed-film baffled bioreactor for wastewater treatment with regard to its energy consumption and production. The total potential of the bioenergy recovery of the bioreactor was evaluated not only from the anaerobic wastewater treatment but also from the produced bio-wasted sludge of both phases. Statistical correlations between bio-methane production and kinetic coefficients were uncovered. Methane yields between 0.15 and 0.30 L CH4.g sCODremoved−1 were obtained during anaerobic wastewater treatment. The maximum energy recoveries from the digestion of bio-wasted sludge (sloughed biofilm) equaled 0.28 and 0.3 L CH4. g TS−1 for aerobic and anaerobic units, respectively. The Grau model was appropriate for predicting the performance of the bioreactor and the potential of bio-methane production. It was demonstrated that substrate utilization rate (Rsu) and Grau coefficient (KG) can be applied to predict the rate of methane production. Regarding the volume of treated wastewater, the energy production was in the range of 2.8–12 kWh.m−3. Moreover, the overall energy consumption of wastewater treatment was in the range of 0.32–0.79 kWh/kg sCODremoved, while the total energy production was 3.7–5.1 kWh/kg sCODremoved. Therefore, the designed bioreactor was energy positive with net energy production of 3.39–4.5 kWh/kg sCODremoved−1. The total energy requirement for both wastewater treatment and bio-wasted sludge digestion was 7–15.5% of the total energy production, and, therefore, the bioreactor is a sustainable energy process. The contribution of anaerobic wastewater treatment and anaerobic digestion of bio-wasted sludge of aerobic and anaerobic units for energy recovery as bio-methane was 53, 26, and 21%, respectively. As the bioreactor achieved more than 95% of sCOD removal and have a high bioenergy production, and since kinetic coefficients demonstrated the considerably high performance of the bioreactor, it can be of interest as an appropriate treatment process.

Model Predictive Control of Stochastic Wastewater Treatment Process for Smart Power, Cost-Effective Aeration

Abstract Wastewater treatment is an essential process to ensure the good chemical and environmental status of natural water bodies. The energy consumption for wastewater treatment represents an important cost for water utilities. Meanwhile has the increasing fraction of renewable energy sources in the electricity market created the possibility of exploiting cheaper (and greener) electricity. This paper proposes model predictive control driven by stochastic differential equations and genetic optimization to prioritize aeration in periods with low electricity prices thereby reducing costs and empowering smart use of green electricity. This is without violation of legislation and equipment constraints. The method is tested with real plant data and electricity market prices to demonstrate efficiency and feasibility.

A novel index of total oxygen demand for the comprehensive evaluation of energy consumption for urban wastewater treatment

In wastewater treatment plants (WWTPs), the majority of energy inputs is consumed by aeration systems to support both the biochemical oxidation of organics and transformation of ammonia-nitrogen into nitrate-nitrogen. Consequently, WWTPs energy efficiency evaluation only based on metrics derived from the organic constituents such as chemical oxygen demand (COD) or biological oxygen demand (BOD) may not reflect the true energy consumption of WWTPs with variable influent quality. Therefore, to overcome this limitation, total oxygen demand (TOD) is introduced in this article, and a novel index EO, namely the energy consumption for the removal of a unit mass of TOD is proposed for evaluating the energy efficiency in WWTPs. Furthermore, by considering the stoichiometric relations of oxygen consumption for the oxidation of both organics and ammonia-nitrogen, methods for calculating the EO are proposed. Using the novel EO index and the available annual operation data of 2022 WWTPs, the current status of energy consumption for wastewater treatment in China were analyzed. The findings show an average EO decrease from 5.2 kWh/kg to 1.2 kWh/kg as the WWTP loading rates increase from 20% to 100%. Also, EO decreased from 4.1 kWh/kg to 1.5 kWh/kg as the average TOD removal increased from 60% to over 90%. Moreover, EO decreased from 2.9 kWh/kg to 1.0 kWh/kg as the WWTP scale increased from less than 10,000 m3/d to over 5,00,000 m3/d. Thus, the energy efficiency of WWTPs increases with increasing loading rates, TOD removal, and scale. Also, the wastewater treatment technology applied influences the EO significantly, especially for small- and medium-size WWTPs with capacities less than 50,000 m3/d which account for circa 76% of all WWTPs in China. The WWTPs applying sequential batch tractors (SBR) tended to show lower average EO (<1.7 kWh/kg) than those applying anaerobic/oxic (A/O), anaerobic/anoxic/oxic (A2/O) and oxidation ditch (DO) (1.9 kWh/kg ≤ EO ≤ 2.0 kWh/kg). Thus, as an index of the energy consumption per unit mass of TOD removed, EO reflects the essence of wastewater treatment for pollutants removal in contrast to other existing energy indices based on the volume of treated wastewater. Moreover, due to the large variability of the WWTPs influent qualities, the TOD contributed by ammonia-nitrogen varied widely between 12.2% and 80.7% of the total TOD. Therefore, EO calculation based on TOD but not merely the organic component (COD or BOD) provides a more comprehensive index for evaluating and optimizing the energy efficiency of WWTPs.

Toward an Energy Efficient Wastewater Treatment: Combining a Microbial Fuel Cell/Electrolysis Cell Anode With an Anaerobic Membrane Bioreactor

Recently, it has been shown that combining a bioelectrochemical system (BES) with an anaerobic membrane bioreactor (AnMBR) to produce electricity can reduce the overall energy consumption of wastewater treatment. In this study, we tested the recently proposed concept that integrates a microbial anode into an AnMBR, under application relevant conditions, for the treatment of synthetic brewery wastewater. We developed two system configurations: a filtering anode with stainless steel filter plate; and a hybrid anode, in which a polymeric membrane is combined with stainless steel mesh. As fouling is problematic in AnMBRs, we investigated the effect of two fouling mitigation methods, namely electrochemical cleaning and application of a turbulence promotor, on the permeate fluxes and current densities. We also investigated the effect of cathode (counter electrode) position on the permeate fluxes and current densities in filtering and hybrid anode. Our results revealed that permeate fluxes were influenced by the membrane pore size; and dropped below 5 L m-2 hr-1 on day 3 with filter grade 0.5 μm; whereas similar values of permeate flux were observed after five days of operation with the membrane with filter grade 0.1 μm. COD removal across the membrane reached up to 644 mg L-1 indicating improvement in energy efficiency and effluent quality of the AnMBR. The location of cathode did not influence permeate fluxes and current densities, but permeate pH was largely affected. Electrochemical cleaning improved permeate fluxes more than two-fold (18.9 L m-2 hr-1 after 7 days of operation) compared to the operation of the 0.1 μm membrane without a cleaning procedure. Application of a turbulence promotor increased permeate fluxes and current densities in filtering anode. The hybrid anode resulted in similar current densities, but higher permeate fluxes as compared to the filtering anode, which dropped below 20 L m-2 hr-1 only after 8 days of operation. The hybrid anode configuration is an attractive option that combines high permeate fluxes on conventional non-conductive filters with current generation on an inexpensive conductive material. In summary, our results demonstrate that combining BES with AnMBR is a promising approach towards an energy efficient wastewater treatment.

Statistical regression modeling for energy consumption in wastewater treatment

Wastewater treatment is one of critical issues faced by water utilities, and receives more and more attentions recently. The energy consumption modeling in biochemical wastewater treatment was investigated in the study via a general and robust approach based on Bayesian semi-parametric quantile regression. The dataset was derived from a municipal wastewater treatment plant, where the energy consumption of unit chemical oxygen demand (COD) reduction was the response variable of interest. Via the proposed approach, the comprehensive regression pictures of the energy consumption and truly influencing factors, i.e., the regression relationships at lower, median and higher energy consumption levels were characterized respectively. Meanwhile, the proposals for energy saving in different cases were also facilitated specifically. First, the lower level of energy consumption was closely associated with the temperature of influent wastewater, and the chroma-rich wastewater also showed helpful in the execution of energy saving. Second, at median energy consumption level, the COD-rich wastewater played a determinative role in the reduction of energy consumption, while the higher quality of treated water led to slightly energy intensive. Third, the higher level of energy consumption was most likely to be attributed to the relatively high temperature of wastewater and total nitrogen (TN)-rich wastewater, and both of the factors were preferably to be avoided to alleviate the burden of energy consumption. The study provided an efficient approach to controlling the energy consumption of wastewater treatment in the perspective of statistical regression modeling, and offered valuable suggestions for the future energy saving.

Simultaneous use of a crossflow filtration membrane as microbial fuel cell anode – Permeate flow leads to 4-fold increased current densities

A new concept for the combination of membrane bioreactors and microbial fuel cells is introduced, that aims at the production of electricity for reducing the overall energy consumption of wastewater treatment. In contrast to previous approaches, the anode is integrated as microfiltration membrane in sidestream crossflow configuration. Using a stainless steel filtration membrane with G. sulfurreducens and an acetate-based synthetic medium, up to 4-fold higher current densities are achieved. In a standard setup without filtration, a membrane of filter grade 1 µm shows current densities of 5.8 A m−2 ± 0.5 A m−2 compared to >11 A m−2 when it is used simultaneously as membrane filter. With smaller pore sizes of filter grade 0.5 µm, 4.4 A m−2 ± 0.5 A m−2 in a standard setup and >15 A m−2 in a filtration setup are achieved. The permeate flow was identified as the main parameter leading to increased current densities.

Performance analysis of a solar photochemical photovoltaic hybrid system for decolorization of Acid Red 26 (AR 26)

To reduce the power energy consumption of wastewater treatment and make full use of the solar spectrum, a new water purification system that integrated homogeneous solar photochemical (SPC) and photovoltaics (PV) was constructed to treat wastewater and generate electricity for the first time. Hydrogen peroxide (H2O2) and potassium persulfate (K2S2O8) were chosen as oxidants in the system and have a comparative analysis. The results show that solar/K2S2O8 has a higher decolorization efficiency than solar/H2O2, the accumulated ultraviolet energy in solar/K2S2O8, needed for complete decolorization, is far lower than in solar/H2O2. Also temperature has a positive effect on the dark-K2S2O8 processes especially in the range of 40–60 °C, and it follows pseudo-first-order kinetic relationship. Meanwhile, to investigate the influence of flow channel on PV, the short circuit current (Isc) and maximum output power (Pm) were monitored. It indicates that the presence of flow channel effectively decreases the working temperature of PV modules, while the Isc and Pm have a different degree reduce. Luckily, the impact is not big. Additionally, Pm in experiment system, though lower than reference system, is sufficient to drive the whole system.

Enzymatic pretreatment of microalgae using fungal broth from Trametes versicolor and commercial laccase for improved biogas production

Coupling microalgae production to wastewater treatment can reduce the costs of microalgae production for non-food bioproducts and energy consumption for wastewater treatment. Furthermore, microalgae anaerobic digestion can be enhanced by applying pretreatment techniques. The aim of this study is to improve the biogas production from microalgal biomass grown in urban wastewater treatment systems by applying an enzymatic pretreatment with crude fungal broth and commercial laccase. To this end, the fungus Trametes versicolor was cultured, and the enzymatic activity of the culture broth analysed by measuring laccase concentration. The results showed that both the fungal broth and commercial laccase pretreatment (100UL−1) over an exposure time of 20min increased the methane yield in batch tests. Indeed, the fungal broth pretreatment increased the methane yield by 74%, while commercial laccase increased the methane yield by 20% as compared to non-pretreated microalgal biomass. In this manner, laccase addition enhanced microalgal biomass anaerobic biodegradability, and addition of T. versicolor broth further improved the results. This fact may be attributed to the presence of other molecules excreted by the fungus.

Determinants of water consumption in the dairy industry

This paper analyzes the correlations between selected technical, process and production factors, equipment profiles and water consumption statistics in four types of dairy plants. Dairy plants were surveyed both individually and in groups. Water consumption was most highly correlated (r &gt; 0.868) with equipment profiles. The highest water consumption was observed in dairy plants operating milk powder departments. In those plants, organization and production factors could significantly reduce water consumption levels because in addition to milk powder, those plants also supplied eight other products. The indicators of water consumption per unit of the final product were correlated (at 0.820 &gt; | r | &gt; 0.663) with equipment profiles, the degree of process automation and employment. Variations in water consumption per unit of the final product were best explained in small plants supplying several products. The presented equations can be used to optimize water demand of various types of equipment and to determine the correlations with energy consumption for wastewater treatment. Our results can contribute to the development of water consumption models in dairy plants and the implementation of clean production standards.

Material and Energy Flow Analysis in Sewage Sludge Incineration and Composting Treatment Processes

This study aims to clarify the material and energy flows in a well-known sewage sludge treatment plant in Japan; the treatment processes include composting, drying, incineration, and incineration with ash melting. We used not only statistical data but also data such as carbon, nitrogen, and moisture content in sludge obtained through our on-site observations. Material and energy flow analysis of sewage sludge composting is seldom reported in comparison with the analysis of other recycling and treatment methods. Therefore, we have performed material and energy flow analysis on sewage sludge composting to estimate factors such as environmental load and energy balance. We investigate the energy consumption of sewage sludge composting in one company that produces manure through aerobic fermentation of sewage sludge. In addition, we compare sewage sludge composting with incineration and evaluate their respective characteristics regarding sewage treatment and production of manure. It has been found that the use of anaerobic digestion of sewage sludge can reduce the overall energy consumption in sewage sludge treatment if power generation using biogas is adopted; however, the digestion of sewage sludge lowers the heating value of the digested sludge, requiring more energy to operate the digester. The energy consumption in a wastewater treatment plant accepting returned water from sludge digestion was increased by 10% to 20% compared to the process without sludge digestion. The overall energy consumption in both wastewater treatment and sludge digestion should be considered. The electric power was 60% of the overall energy consumption and 70% of the energy consumption in the plant's production sector.