Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1101-1106  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal web link:  
Effect of Electromagnetic Field on Low Dissolved  
Oxygen Wastewater Treatment  
Nulhazwany Abdul Malik, Khalida Muda, Nur Syamimi Zaidi, Mohamad Darwish*, Ahmad  
Hanis Omar@Omri  
School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia (UTM), 81310, Johor Bahru, Malaysia  
Received: 13/03/2020  
Accepted: 07/07/2020  
Published: 20/09/2020  
Activated sludge (AS) system is a biological treatment process that is widely applied in municipal wastewater treatment. Concentration  
of the dissolved oxygen (DO) is one of the important parameters that may influence the performance of AS system. Thus, certain levels of  
DO in AS systems should be maintained to achieve high efficiency of pollutants removal. However, the energy consumption of aeration stage  
represents approximately 50% of total demand of AS system. Therefore, reducing aeration energy would improve the feasibility of AS  
process. This study investigated the enhancement of AS process under low DO condition using electromagnetic field (EMF). The AS was  
exposed to EMF at intensity of 3 mT with DO concentrations of 1 and 2 mg/L for 24 hours. The impact of EMF on the biomass concentration,  
settling velocity, sludge volume index and pollutants removal were thoroughly investigated. The results indicated significant improvement  
in the physical properties of AS exposed to the EMF, which resulted with high accumulation of biomass concentration. The settling velocity  
and sludge volume index value of the biomass at the end of the experiment were 95 m/h and 72.6 mL/g, respectively. The reactor exposed to  
EMF under 2 mg/L of DO showed the highest removal efficiency of chemical oxygen demand (80%) ammonia (97%), nitrite (99%), and  
total nitrogen (84%). Additionally, it was proved that EMF could enhance the settleability of the AS in the treatment system.  
Keywords: Electromagnetic field, Activated sludge, Biomass, Nitrate, Ammonia nitrogen  
Generally, most of the mentioned treatment processes have shown  
significant improvements under specific magnetic applications (4  
Activated sludge process is one of the aerobic biological  
treatment methods, which is employed as a core process in more  
than 90% of the municipal wastewater treatment plants (12). Yet,  
due to the fluctuation of wastewater quality and flow,  
conventional activated sludge shows a variety of drawbacks,  
including sludge expansion, loose flocs structure as well as  
biomass deficiency (13). In addition, the energy consumed by the  
aeration process represents approximately 50% of the total energy  
usage of the activated sludge process, which can be dramatically  
reduced by decreasing the operating dissolved oxygen (DO)  
concentration (14). However, according to Holenda, Domokos  
The rapid development of humans' communities leads to huge  
increase in wastewater generation (1). Population explosion and  
expansion of urban areas raise the adverse impacts on water  
resources, especially in regions where natural resources are  
restricted. This phenomenon reflects the significant growth in  
default volumes of wastewater, which makes it an urgent  
imperative to develop effective and affordable technologies for  
wastewater treatment (2).  
Recently, a tremendous increase in the applications of  
electromagnetic fields (EMFs) appeared in different domains  
including therapeutic and diagnostic medicine, environmental  
managements, and industrial procedures (3). Magnetic  
technology is a physical treatment technique that was introduced  
to avoid the consumption of chemicals such as polyphosphates or  
corrosive substances, which are expensive and can be harmful to  
the environment and most importantly, human health. This  
technology has been implemented in various ways through the  
application of either permanent magnets or high-gradient  
magnetic separation (HGMS) in combination with magnetic  
seeding or magnetic adsorption (4). To date, magnetic field was  
applied for the removal of heavy metals (5), organic compounds  
(15), DO levels in the aerobic reactors have significant influence  
on the behaviour and activity of the heterotrophic and autotrophic  
microorganisms that live in the AS system.  
Limitation of DO concentration often results in poor  
flocculated sludge and more turbid effluents (16). On the other  
hand, an excessively high DO, which requires a high air flow rate,  
leads to a high energy consumption, and may deteriorate the  
sludge quality as well. Moreover, high DO concentration in the  
internally recirculated water reduces the efficiency of  
denitrification process. To the best of our knowledge, the  
enhancement of municipal wastewater treatment using EMF  
(6, 7), nutrients consisting of nitrogen and phosphorus  
compounds (8, 9) and turbidity and suspended solids (10, 11).  
Corresponding author: Mohamad Darwish, School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia (UTM),  
1310, Johor Bahru, Malaysia. Email:  
Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1101-1106  
under the condition of low DO concentration was never tested  
before. The present study was therefore aimed at investigating the  
feasibility of applying an EMF in maintaining high effluent  
quality in municipal wastewater treatment under low  
concentration of DO. Specifically, objectives of this study are: (1)  
to identify the effect of EMF on the physical properties of  
municipal wastewater (i.e. mixed liquor suspended solids  
(MLSS), mixed liquor volatile suspended solids (MLVSS),  
settling velocity and sludge volume index (SVI)); and (2) to  
analyse the impact of EMF on the removal of chemical oxygen  
demand (COD), ammonia, nitrite, nitrate and total nitrogen (TN).  
Materials and methods  
.1 Municipal wastewater characteristics  
Figure 1: Schematic diagram of the experimental setup (1: DC Power  
supply, 2: Crocodile clip, 3: Column, 4: Stone diffuser, 5: Copper coil, 6:  
Retort stand, 7: Tube, 8: Aquarium pump)  
Raw samples of municipal wastewater, as well as sludge  
biomass, were collected twice a week from a sewage treatment  
plant and stored under 4°C. Table shows the main  
characteristics of municipal wastewater used in this study.  
.3 Analytical methods  
The concentrations of MLSS and MLVSS were measured  
based on Methods No. 2540D and 2540E, respectively (APHA,  
005). The settling velocity was determined by recording the  
average time taken for the individual sludge to settle at a certain  
height in a glass column filled with tap water (17). In this study,  
a 16 cm glass column was used to test the settling velocity. Total  
nitrogen, COD, nitrite, and nitrate concentrations were measured  
using HACH (DR 6,000) spectrophotometric standard methods,  
while ammonia nitrogen was analysed using Nessler method.  
Table 1: Characteristics of municipal wastewater  
Temperature (°C)  
COD (mg/L)  
Ammonia (mg/L)  
Total Nitrogen  
.2 Experimental setup  
Figure 1 shows a schematic diagram of a sequential batch  
Results and discussion  
.1 Effect of EMF on wastewater physical properties  
reactor (SBR) used in this study. The SBR consists mainly of  
three identical glass columns (Column A, B and C) with a total  
volume of 1,300 mL for each column. A copper coil was attached  
to Column B and C (Figure 1), which supplied the EMF with an  
intensity of 3 mT, while Column A was not exposed to EMF and  
kept as a control. Each column was supported with a stone air  
diffuser located at the bottom of the column, to provide the system  
with the required aeration. The concentrations of DO in Column  
A, B and C were maintained at 3, 2 and 1 mg/L, respectively. The  
level of DO concentration was monitored using YSI dissolved  
oxygen meter (USA). The aeration intensity was continuously  
monitored to ensure that the level of DO concentration was within  
the specified range. During the start-up period, 200 mL of  
activated sludge and 800 mL of raw municipal wastewater were  
added into each column, to compose a working volume of 1,000  
mL with a total biomass concentration of 2,000 mg/L. The cycle  
time of the SBR was 24 hours, consisting of 2 min for feeding  
reaction, 23.4 h for aerobic reaction, 30 min for settling and 2 min  
for discharge.  
The physical properties observed in this study included  
biomass concentration, settling velocity and SVI.  
.1.1 Biomass Concentration  
The profile of biomass concentration (MLSS and MLVSS) is  
given in Figure 2(A) and (B). Generally, it can be seen that the  
MLSS in Column B was higher than in Column A and C. The  
average of MLSS for Column B was 2425±33.2 mg/L, while in  
Column A and B the average was 1,720±28.3 and 1,625±7.2  
mg/L, respectively. At steady state, MLVSS for Columns A, B  
C were 368.6±5.8, 438.6±5.8 and 238.6±5.8 mg/L,  
respectively. Throughout the experiment, both MLSS and  
MLVSS in Column B showed stable reading. Meanwhile, in  
Columns A and C, sudden drops were observed in the middle of  
the experiment. The high MLSS and MLVSS in Column B was  
probably due to the effect of EMF applied to Column B.  
Principally, magnetic field could influence the microbial  
community composition and metabolisms, which could further  
affect the biomass characteristics (18-20).  
According to  
For the physical characteristic’s determination, the samples  
were collected once a week at the middle part of the glass column,  
and were used to analyse MLSS, MLVSS, settling velocity and  
SVI. With regards to the performance analysis, the samples were  
collected twice a week and centrifuged for 5 minutes at 6,000  
rpm. The supernatant was used to measure the removal  
performance of COD, ammonia, nitrite, nitrate and total nitrogen.  
Zieliński, Cydzik-Kwiatkowska (21), this higher concentration in  
biomass resulted from the improved absorption and coagulation  
in the sludge particles due to the effect of magnetic field. In  
Column A (no EMF exposure), the molecules moved in random  
manner, while in Column B and C, the exposure to magnetic field  
allowed the molecules to align easily according to their positive  
and negative charges. Consequently, the molecules were arranged  
orderly, thus able to induce coagulation (22).