Waste Water Silt produces surplus value

The demands for reduced emissions of greenhouse gases have increased the use of biofuels and other waste produced fuels in electricity producing combustion facilities. But those kinds of fuel are hard to combust and cause, among other things, corked up bed bolier systems and costly disturbances in operation.

- I have primarily been examining fuels and ashes, various kinds of waste fuels, i.e. everything from straw to combustable sorted waste from households and waste water silt, says Anita Petterson.
The driving force behind her research has primarily been her desire to be part of the development in the energy sector.
- We need to work towards a sustainable development.

New Methods are Important

The first part of her work is about phosphorus retrieval from ashes that are the result of combusting waste water silt and wood pellets. She has tried to find a simple way of extracting phosphorus for recycling while simultaneously not extracting heavy metals. Phosphorus is used as a fertilizer.
- Normally phosphorus is extracted from the apatite mineral, prevalent in Russia, Finland, the USA and Africa among other places. Phosphorus is used for making artificial fertilizers. But the amount of apatite on earth is limited and is calculated to last only for another hundred and thirty years or so. The phosphorus hitherto extracted is spread all over. Therefore, we need to start extracting phosphorus from the ecocycle, explains Anita Pettersson.

Detergents are Good

The other part of the dissertation is about alkali and chlorides (sodium and potassium), that cause problems in bed boilers by leaving coating which in turns leads to corrosion, and sintring which corks up the bed boilers. That kind of problem leads to costly production stops. Anita Petterson has examined co-combustion of various fuels in order to see if there is a simple way of solving the problems. Her results show that if waste water silt is added to the combustion process, the problems disappear.
- I have look at the mechanisms that affect the process and reached the conclusion that there are aluminium silicates in the silt. The aluminium silicates come from household detergents and these aluminium silicates contain zeolites that attract alkali, i.e. potassium and sodium. When the silt is incinerated the biproducts are not harmful alkali chlorides but instead hydrochloride which does not stick and can easily be trapped using limestone in the smoke filter.

Another important part of work has been looking at methods for predicting the characteristics of various fuels when they are combusted.
Another very topical question now that various kinds of waste are used for energy production; do you live as you learn?
- Yes, I try! At home we burn pellets for heating, use solar power and drive an ethanol-fuelled car, and we use low energy lamps.

Reeducated Herself from Caregiving to Technology

Anita Petterson is 43 years old and comes from Seglora just outside Borås. Her career leading up to her present research work has been far from straight. Before she even considered becoming an engineer she worked at a daycare center and as an assistant nurse. Originally, she was going to pursue a career as a nurse, but the caregiving profession went through a slump, and she already had an interest in technology.
- My father is very interested in technology and he has taught me that having the audacity to both try and fail is good.

Anita Petterson decided to reeducate herself. She enrolled at the Viskadalen folk high school to study math. After that she took a base year of studies in technology at the School of Engineering at the University of Borås. She took a degree in electrotechnology, electric power and heat technology, in the year 2000. She felt so good about it that she continued with a two-year master programme in the field and took her next degree in the 2002. Then it was of to post-grad studies.

After the dissertation she will continue her research and teaching.


The title of her dissertation is 'Characterisation of Fuels and Fly Ashes from Co-Combustion of Bio- and Waste Fuels in a Fluidised Bed Boiler – A Phosphorus and Alkali Perspective'

Public disputation
Date: the 15th of October
Time: 11 a.m.
Location: Room HC4, Hörsalsvägen 14, Göteborg
Faculty opponent: Professor Mikko Hupa of the Åbo Academy University in Åbo, Finland.

The disseration will be held in English.

Read the disseration in BADA.