Performance comparison of conventional biological treatment process and membrane bioreactor treating common industrial effluent

Abstract

Industrial effluent is challenging for wastewater treatment plants due to its complexity, toxicity and variable composition. This study aimed to evaluate the efficiency of industrial wastewater treatment between a lab-scale membrane bioreactor (MBR) and a full-scale anoxic/oxic (A/O) process. The wastewater used was after primary sedimentation tank, which involved lime or ferric coagulant. The results showed that the treated water quality from both systems was satisfied the national effluent standard for wastewater (column B of QCVN 40-MT:2011/BTNMT). The effluent from A/O process contained 74 ± 11 mg/L of COD, 8.3 ± 1.9 mg/L of TN, 1.6 ± 0.6 mg/L of TP, and 201± 38 Pt-Co of color. Meanwhile, the concentrations of COD, TN, TP, and color in the effluent of MBR system were 88 ± 21, 23.2 ± 4.6, 0.3 ± 0.2 mg/L, and 220 ± 98 Pt-Co, respectively. The removal rates of COD, TN, TP and color of anoxic/oxic process were 234 ± 119, 16 ± 3, 0.3 ± 0.2 mg/L.day, 213 ± 58 Pt-Co/L.day, respectively. The removal rates of COD, TN, TP, and color in MBR system were 1.6, 1.3, 10.3, and 2.1 times higher than those in the A/O process, respectively. Although the A/O process in industrial zones performed well, the MBR system demonstrated higher removal rates, particularly for nutrient removal. Besides, MBR systems offer several advantages, including reduced excess sludge production and less space requirements compared to A/O process. In general, MBR offers a promising solution for industrial wastewater treatment, with strong potential for application in industrial zones.

Introduction

Clean water resources in Vietnam are threatened due to the rapid economic expansion and the discharge of most untreated industrial wastewater to water bodies 1 . Industrial parks in Vietnam have been widely developed, leading to the emergence of many factories with various production processes. The industrial fields generating toxic wastewater including textile and dyeing, pharmaceutical production, paper, and printing 2 . This increases the danger of polluted water sources as a result of discharge from industrial zones (IZs) 3 . More than 400 industrial parks are throughout the country as of July 2024, which discharge about 3 million m ³ /d wastewater 1 . Since 2009, all industrial wastewater from IZs must be collected and treated at a central wastewater treatment plant (WWTP), and the treated wastewater must meet Vietnam's national technical regulation on industrial wastewater, QCVN 40:2011/BTNMT 4 . In 2018, 88% of the IZs had WWTP, and 71% of the wastewater was treated for at least some parameters such as COD, heavy metals 4 . Large volumes of wastewater, including hazardous heavy metals, phenolic organic compounds, and other persistent organic pollutants, are released by major polluting industries including the textile, paper, printing, and dyeing sectors 2 . Industrial wastewater contains a variety of substances at varying concentrations, treating industrial wastewater is a complicated process. Pre-treatment, primary, secondary, and tertiary, refining, and purification are the categories into which they are generally accepted in industrial wastewater treatment 5 . For industrial wastewater treatment, physical processes, e.g., screening, filtration, sedimentation, and membrane filtration. The primary treatment methods comprised precipitation, ion exchange, adsorption, photocatalysis, and electrochemical process. Different technologies are used to treat industrial wastewater which has their pros and cons. The precipitation methods are cost-effective (low cost and easy for operation with mostly metals can be removed). However, this method generates a large amount of sludge, leading to complications in management. On the other hand, ion exchange technology includes material regeneration and its selective property for metal ions. In contrast, the drawbacks of this method are the limited number of metal ions available and the high cost 6 . In terms of electrochemical method, it can remove most of the metals with no chemical consumption. Electrodialysis method is high separation efficiency with low chemical use. However, these methods have high operational costs due to energy consumption. Furthermore, membrane fouling in electrodialysis also leads to additional operational cost 6 .

As a result, biological wastewater treatment is preferred for industrial wastewater due to its low energy consumption, high efficiency, and ability to overcome the limitations of other conventional approaches 7 . Membrane biological reactors are one of the alternative methods available for wastewater treatment. Membrane bioreactor technology (MBR) combines biological treatment and membrane filtration to provide advanced wastewater treatment with activated sludge and attached growth are two biological processes. Membrane filtration in MBRs separates microbes and degraded substances, improving efficiency and selectivity. It has potential for generating quality effluent and treating industrial wastewater, such as fish canning, protecting water resources and promoting water reuse. MBRs can reduce certain pollutants, such as the diclofenac metabolite four-hydroxy diclofenac. The MBRs would be a good selection for industrial wastewater treatment. Longer sludge retention time (SRT) increases the concentration of the activated sludge, resulting in high-efficiency 8 . The improved membrane filtration and biological degradation make the effluent quality good and steady, smaller footprint, low chemical consumption are also advantages of MBR. However, the main disadvantage of MBR technology is membrane fouling and the inability to remove micropollutants because the membrane pore size used in MBR technology cannot trap them. This study aims to investigate the treated effluent qualities of the anoxic/oxic process (A/O process) and membrane bioreactor (MBR), seeking to determine which method is more effective and sustainable for industrial wastewater treatment. By comparing these technologies, the research provides valuable insights for industries in selecting the most appropriate treatment method based on performance, energy consumption and environmental impact.

MATERIALS AND METHODS

Central wastewater treatment plant (A/O process) at an industrial zone

The central wastewater treatment plant (WWTP) was investigated with a design capacity of about 4000 m ³ /d. The main biological treatment technology is anoxic/oxic process (A/O process). The main industrial factories include dyeing and textile, mechanical engineering, leather and footwear, food processing, electro-plating industries. Most factories have their own pre-treatment system that meet the industrial zone’s standards (TCVN 5945:2005, Column C) before discharging into WWTP respondsible for treating the entire zone’s wastewater.

The WWTP includes main treatment processes such as equalization tank (EQ), primary physicochemical process (PC1), anoxic/oxic process (A/O), secondary physicochemical process (PC2), and disinfection.

The WWTP was operated at an organic loading rate (OLR) of 0.48 kgCOD/m ³ .d. The hydraulic retention time (HRT) was 1.89 days, and sludge retention time (SRT) is 22.5 days.

Lab-scale membrane bioreactor system (MBR)

The wastewater used in this study was taken from after 1 ^st physical-chemical process (PC1) of a central wastewater treatment plant. The pH of wastewater ranged from 7.1 to 8.3. The color concentration was 171 - 414 Pt-Co while the TSS, COD, TN, and TP concentrations were in range of 24 - 184, 141 - 480, 25.27 - 40.24, and 0.25 - 0.81 mg/L, respectively ( Table 1 ).

Table 1 Characteristics of Influent wastewater

A lab-scale system of membrane bioreactor (MBR) with a volume of 10.5 L (0.30 m length x 0.07 m width x 0.50 m height) in which the working volume is 8.0 L. The polyethersulfone (PES) flat sheet membrane with a surface area of 0.05 m ² and pore size of 0.1 µm was supplied by MARTIN Membrane system Co. Ltd (Germany). MBR was operated at an organic loading rate (OLR) of 0.54 kgCOD/m ³ /d. The permeate flux and hydraulic retention time (HRT) of MBR were 6.0 L/m ² /h (LMH) and 12.8 h, respectively. Permeate pump operation was cyclic (6 minutes-filtration, 4 minutes-relaxation). The digital pressure gauge was installed to daily record the transmembrane pressure (TMP). The sludge retention time (SRT) was maintained at 20 days during operation.

Analytical methods

The parameters of Total Suspended Solid (TSS), Chemical Oxygen Demand (COD), color, Total Nitrogen (TN), and Total Phosphorus (TP) were analyzed following methods in Standard Methods 9 . Besides, pH value was monitored with a portable meter HI 9813–6 (Hana, Romania)

RESULTS AND DISCUSSION

Treatment performance A/O process and MBR system

The results clearly present a detailed comparison of treatment performance between the A/O process and MBR, focusing on three factors: organic compounds (COD), nutrients (total nitrogen and total phosphorus), and other parameters (pH and color) show in Figure 1 . Table 2 provides the removal rate for these parameters in both system.

Table 2 Removal rates of main parameters in A/O process and MBR system

Figure 1 . Water quality parameters of A/O process and MBR system: pH, COD, total nitrogen, total phosphorus, and color

Treatment performance A/O process and MBR system

The results clearly present a detailed comparison of treatment performance between the A/O process and MBR, focusing on three factors: organic compounds (COD), nutrients (total nitrogen and total phosphorus), and other parameters (pH and color) show in Figure 1 . Table 2 provides the removal rate for these parameters in both system.

Table 2 Removal rates of main parameters in A/O process and MBR system

Figure 1 . Water quality parameters of A/O process and MBR system: pH, COD, total nitrogen, total phosphorus, and color

Treatment performance A/O process and MBR system

The results clearly present a detailed comparison of treatment performance between the A/O process and MBR, focusing on three factors: organic compounds (COD), nutrients (total nitrogen and total phosphorus), and other parameters (pH and color) show in Figure 1 . Table 2 provides the removal rate for these parameters in both system.

Table 2 Removal rates of main parameters in A/O process and MBR system

Figure 1 . Water quality parameters of A/O process and MBR system: pH, COD, total nitrogen, total phosphorus, and color

Treatment performance A/O process and MBR system

The results clearly present a detailed comparison of treatment performance between the A/O process and MBR, focusing on three factors: organic compounds (COD), nutrients (total nitrogen and total phosphorus), and other parameters (pH and color) show in Figure 1 . Table 2 provides the removal rate for these parameters in both system.

Table 2 Removal rates of main parameters in A/O process and MBR system

Figure 1 . Water quality parameters of A/O process and MBR system: pH, COD, total nitrogen, total phosphorus, and color

Treatment performance A/O process and MBR system

The results clearly present a detailed comparison of treatment performance between the A/O process and MBR, focusing on three factors: organic compounds (COD), nutrients (total nitrogen and total phosphorus), and other parameters (pH and color) show in Figure 1 . Table 2 provides the removal rate for these parameters in both system.

Table 2 Removal rates of main parameters in A/O process and MBR system

Figure 1 . Water quality parameters of A/O process and MBR system: pH, COD, total nitrogen, total phosphorus, and color

Treatment performance A/O process and MBR system

The results clearly present a detailed comparison of treatment performance between the A/O process and MBR, focusing on three factors: organic compounds (COD), nutrients (total nitrogen and total phosphorus), and other parameters (pH and color) show in Figure 1 . Table 2 provides the removal rate for these parameters in both system.

Table 2 Removal rates of main parameters in A/O process and MBR system

Figure 1 . Water quality parameters of A/O process and MBR system: pH, COD, total nitrogen, total phosphorus, and color

Strengths and Challenges

Based on above mentioned, MBR can be a promising method for industrial wastewater treatment and provide stable high-quality treated water. Jijingi et al. 21 demonstrated that MBR technology has been an appropriate approach to improving industrial wastewater quality in developing countries where industrial wastewater is becoming more challenging. Based on this study and previous studies, MBR technology is qualified to remove ordinary pollutants (COD, TN, TP, TSS, and color), suspended solids, oil, grease, even microplastics, heavy metals, pathogens, and emerging pollutants 1 , 21 , 22 . Then, high-quality effluents from MBR technology can satisfy discharge regulations and be utilized for various reuse purposes. In addition, MBR technologies are compact and modular systems so they are a suitable choice for densely populated areas with limited space 21 . Sludge production from MBR technologies has also been reduced to less than that of conventional processes. MBRs offer valuable economic benefits through reduced water consumption, lower environmental impact, and potential revenue from treated water reuse 21 .

However, MBR has some obstacles in the operating period: such as membrane fouling, energy consumption, capital, and operational cost 23 . Energy used in MBR is mainly consumed for aeration (membrane scouring and biological aeration), liquid pumping (lifting and recirculation), sludge mixing, and so forth. Based on the optimization level, size, and operating conditions of the plant, the average energy requirement for MBR operation ranges from 0.4 to 2.3 kWh/m ³ of treated effluent 13 . The capital and operating expenses of MBR are still higher than those of conventional activated sludge without tertiary treatment though comparable to conventional activated sludge with tertiary treatment 23 . Membrane fouling is a significant obstacle in MBR systems. Membrane fouling is mostly a reason for causing energy consumption and affecting the long-term stability of MBR. Improvements in membrane fouling resistance and longevity have led to higher treatment performance, fewer maintenance requirements, and lower operational cost 21 , 23 . Managing these difficulties is thus critical to ensuring the stable, efficient, and long-term operation of MBR systems and their full-scale applicability.

Conclusions

In this study, the performance of a full-scale anoxic/oxic (A/O) process in industrial zones and a lab-scale membrane bioreactor (MBR) system was evaluated for industrial wastewater treatment. The results demonstrated that both systems were effective in reducing pollutants to levels compliant with former national effluent standard (TCVN 5945:2005, Column C). However, the MBR system exhibited significantly higher removal rates for COD, TN, TP, and color compared to the A/O process, particularly in nutrient removal. It is suggested that MBR system holds great promise as an industrial wastewater treatment solution due to its advantages of stable, high-quality effluent, less space requirement, and low sludge production. However, challenges such as membrane fouling, high operational costs, and limited micropollutant removal must be solve to fully optimize MBR technology for larger-scale applications.

LIST OF ABBREVIATIONS

IZs: industrial zones

WWTP : central wastewater treatment plant

MBR: Membrane bioreactor

A/O: anoxic/oxic process

SED: specific electricity demand

PAC: Powder-Activated Carbon

SRT: sludge retention time

EQ: equalization tank

PC1: primary physicochemical process

PC2: secondary physicochemical process

PES: polyethersulfone

Acknowledgements

This research is funded by Vietnam National University Ho Chi Minh City (VNU-HCM) under grant number NCM 2021-20-01.

Competing Interests

The authors declare that they have no conflict of interest.

Authors' Contributions

Sampling, sample analysis, investigation, software, writing - original draft, writing - review & editing: Cong-Sac Tran, Pham-Yen-Nhi Tran, Thi-Yen-Phuong Nguyen, Mai-Nhu Hoang;

Data curation, conceptualization, methodology, writing - review & editing: Phuong-Thao Nguyen, Quang-Huy Hoang, Mai-Duy-Thong Pham; Thi-Tuyet-Nhung Hoang, My-Le Du

Supervision, conceived, designed the methodology, writing - review & editing: Thi-Kim-Quyen Vo, Xuan-Thanh Bui.