PhD: Removing manganese as pre-treatment to limit (bio)fouling in oligotrophic conditions


Leeuwarden, Netherlands 🇳🇱

Manganese (Mn) is the second most common trace metal on earth after Iron, and a critical micronutrient required for the growth and survival of many living organisms. It is found naturally in groundwater, surface water, freshwater, and seawater, mostly as soluble Mn (Mn2+). In the presence of oxidizing agents (abiotic or biotic) and changes in pH, Mn is oxidized to insoluble Mn (Mn3+, Mn4+, or even Mn with a higher oxidation state, depending on the oxidizing agents present). During different water treatment processes, such as in drinking water production, the accumulation of insoluble Mn oxides can result in membrane fouling, recognizable by the black coloration of the fouling layers, often causing irreversible fouling. The conventional drinking water treatment process has a relatively low removal performance of Mn. Manganese oxidizing bacteria (MOB) are microorganisms able to remove Mn2+ efficiently and selectively from water by converting the soluble Mn into manganese oxides (Mn oxides) in oligotrophic environments. This biotic mechanism is so ubiquitous that the majority of naturally occurring environmental Mn oxides are believed to be derived from biogenic Mn2+ oxidation. The mechanism however is poorly understood, as well as the enzymes involved. Our recent research on a real-scale plant producing ultrapure water from wastewater has shown that introducing biological filtration as pre-treatment was protecting the reverse osmosis (RO) units from significant/irreversible biofouling. In such biological filters, Mn2+ was continuously and completely removed by a wide array ofMOB, able to grow as a biofilm on top of activated carbon granules. As a result, black Mn oxides formed within the biofilm, while the water reaching RO units was depleted from Mn2+.

Research challenges
In this project, we want to investigate if the complete removal of manganese can be the key to limit/avoid (irreversible) biofouling in many engineered systems (reverse osmosis, ultrafiltration, cooling towers, etc.). A key step is to understand whether the already formed black manganese oxides are attracted to the membrane surface and triggering the irreversible fouling, or if they are formed from Mn2+ by MOB growing as biofilm layer on top of the membranes/surfaces. In the latter case, manganese can be seen as a fundamental (micro)nutrient for microbial growth (and thus for biofouling) in oligotrophic conditions, and thus the introduction of a biological treatment rich in MOB upstream can avoid their growth in the following steps.

Your assignment
The main objective of the project is producing knowledge to introduce highly selective manganese biological removal as a common practice in many engineered systems such as reverse osmosis, ultrafiltration, cooling towers, etc., to avoid irreversible fouling where oligotrophic conditions apply. This project requires a multidisciplinary approach ranging from microbiology to mathematical modelling.

In the first phase of the project, your will investigate biological manganese removal using mixed microbial communities from engineered systems enriched in MOB, testing the different influencing operational parameters such as oxygen, pH, etc., to optimize their activity and calculating related manganese removal kinetics. You will also asses the microbiological level using several analytical, molecular biology, and microscopy techniques.

In the second phase, you will evaluate the fouling phenomena by means of applied optical and microscopy techniques (OCT, SEM-EDX, CLSM, etc.) and apply modelling to predict the effects of the manganese removal process. Additionally, you will evaluate the possible recovery of Mn oxides for application in other wastewater treatments such as catalysts, sorbents, and electrical conductors.

Your profile
We are looking for a student holding an MSc degree in microbiology, biotechnology, environmental technology/engineering or equivalent, with an interest in modelling. Additional knowledge in inorganic chemistry, microscopy, and/or water treatment processes is desirable. You are able to work in a multi-disciplinary, international team. You have experience with lab work and setup building. Your English is fluent, both written and spoken.

Keywords: manganese oxidising bacteria, biofouling, biological filter, manganese, bioprocess engineering

Supervisory team: Prof. Dr. Ir Cees Buisman (Wageningen University), Dr. M. Cristina Gagliano (Wetsus), Dr. Amanda Larasati (Wetsus)

Project partners: Biofilms theme

Only applications that are complete, in English, and submitted via the application webpage before the deadline will be considered eligible.

Guidelines for applicants:





IHE Delft MSc in Water and Sustainable Development