Influence of Wastewater DOM Fractions on the Adsorption of Pharmaceuticals onto Activated Carbon

Abstract

Micropollutants in our sources of freshwater is an issue which requires immediate attention. The presence of pharmaceuticals, endocrine disrupting agents, pesticides and other harmful compounds have proven to have impact on the aquatic as well as on human life. Treated wastewater being a major source of ingress of micropollutants into the aquatic environment, the current standards do not stipulate any significant restriction on discharge but focuses on the monitoring. This is majorly due to two reasons, lack of understanding about the different compounds and available treatment options are not fully investigated.
Dissolved organic matter (DOM) in the wastewater has proven to have significant impact on the treatment processes designed to remove micropollutants. Even the DOM are less toxic, they often enable transport for various toxic substances such as pharmaceuticals if not treated. In case of activated carbon, DOMs compete with micropollutants for sorption on active sites. Micropollutants have different characteristics and therefore, to optimize these processes, a deeper understanding about the influent along with the treatment process itself is important.
This research focus on the elimination of dissolved organic carbon (DOC) based on size exclusion and hydrophobic/hydrophilic fraction and its effect on the removal of pharmaceuticals using activated carbon. In this research, membrane filtration was used to eliminate DOC and based on elimination of different size fractions, the performance of removal of pharmaceuticals using powdered activated carbon was evaluated. It was observed that the effect of DOC on the treatment is not only a function of molecular weight distribution but the presence of hydrophobicity/hydrophilicity in the wastewater. To study this, the wastewater was fractionated to remove hydrophilic and hydrophobic fractions using a rapid fractionation method and the effect of removal of one fraction on the competition for removal of pharmaceuticals was studied.
The study affirms the finding by various researchers that the presence of high molecular weight compounds (>25 kDa) does not considerably affects the performance of activated carbon for removal of pharmaceuticals but a significant impact was observed due to the competition by low molecular weight compounds. Another important part of the study was to comprehend the effect of hydrophobicity and hydrophilicity and the study indicates that the presence of hydrophobic compounds contributes to most of the competition with pharmaceuticals for sorption on activated carbon. Furthermore, the study also suggests that the use of DOC concentrations of wastewater to evaluate the dosing requirements of activated carbon for efficient removal of pharmaceuticals may not be a good practice.

Popular Abstract

Do we really understand the wastewater enough to remove micropollutants?
Water is an important aspect of our lives. Up to 60% of our body is made up of water. Therefore, to take care of our body we need to supply it with quality products. We often take the quality of water for granted and trust on our municipalities to provide us with good quality water. The treatment of water is a complex process but if something goes wrong, consumers can easily identify it such as bad smell, taste or often colour. But there are more things present in the water that we should be worried about than just these.
A micropollutant is a manmade compound which has several impacts on the environment including aquatic ecosystem and human being. Even though these compounds are not found to cause acute conditions, consumption at low concentrations for a very long time may induce chronic diseases. We drink water on daily basis and these compounds accumulate in our body, a process called biomagnification. The sources of the micropollutants are anthropogenic i.e. we use them as pesticides, domestic cleaning agents, chemicals used in industries, etc. Especially, medicines which are anti-inflammatory, antibiotics, etc. contain certain active substances such as diclofenac and sulfamethoxazole which after consumption end up in our faeces or urine which ultimately reach the wastewater treatment plants. These compounds are very stable and require specialized removal methods. But once released in the environment, they are diluted. Water being a circular system, these micropollutants end up in the drinking water treatment plants. Due to extreme low concentrations, it is hard and costly to treat water for these compounds. Therefore, it is more beneficial to remove the micropollutants from the wastewater than from drinking water. But it is a hard task to undertake. Wastewater treatment plants have complex treatment systems than water treatment plants. Treatment of micropollutants is a part of the problem. It is often recognised that we have not established all of the micropollutants present in the wastewater because it is impossible given the compounds have multiple sources and could undergo various transformations to form new compounds. Various researchers focus on the development of treatment options whereas, some focus on understanding the characteristics of the wastewater and micropollutants itself. In this research, the focus is on the both sides as it is important to understand the features of the wastewater and use it to optimize the performance of the treatment selected for the removal of micropollutants.
The wastewater is composed of various organic material including human faeces. These are referred to as total organic matter. Total organic matter is further divided into two parts which are particulate and dissolved organic matter. Most of the particulate and some dissolved organic matter is removed in primary treatment steps. The rest of the dissolved organic matter along with micropollutant requires additional treatment. There are various methods used but this research was focused on the membrane filtration and activated carbon. Membrane filtration is a filtration method which removes some compounds based on their size. Each membrane has pores and allows smaller compounds to pass through but retains bigger compounds. Activated carbon works as a sticky surface which allows micropollutants to attach (adsorb). Activated carbon does not selectively allow the micropollutants to adsorb but all of the compounds including the organic matter can adsorb onto the surface. The removal by activated carbon depends upon the competition between the compounds. Therefore, the understanding about the affinity of these compounds towards the activated carbon is an important aspect investigated in this study.
Wastewater contains different compounds with different properties. In this research, they are divided as hydrophobic and hydrophilic compounds. Hydrophilic compounds are in completely dissolved state whereas hydrophobic are partially separate from dissolved state. On activated carbon, the hydrophobic compounds quickly adsorb onto the surface and reduces the surface available for micropollutants. This is a major problem in the use of activated carbon for removal of micropollutants. Most of the researchers estimate the requirement of activated carbon based on the concentration of dissolved organic matter. But it may not represent the various compounds with different properties present in the wastewater. Therefore, this research seeks to understand the effect of hydrophobic/hydrophilic compounds present in the wastewater and probes the current practices used to maximize removal of micropollutants.

• author: Karande, Koustubh
• supervisor: Per Falås; Michael Cimbritz
• organization: Chemical Engineering (M.Sc.Eng.)
• course: VVAM01 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Wastewater treatment, Dissolved organic matter, Pharmaceuticals, Activated carbon, Hydrophobicity, Molecular weight, Water resources engineering
• report number: 2022-05
• language: English
• id: 9086998
• date added to LUP: 2022-06-13 11:58:51
• date last changed: 2022-06-13 11:58:51