Effect of Electromagnetic Field on Low Dissolved Oxygen Wastewater Treatment

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 1101-1106

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

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

Abstract

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

Introduction¹

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: sjmohamad@utm.my.

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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

Parameter

Temperature (°C)

Values

22-27

8.1

COD (mg/L)

Ammonia (mg/L)

Total Nitrogen

103-431

18.25-41.5

24-74

(mg/L)

.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

and

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).

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