Wastewater treatment using microalgae

Wastewater tre a tm e n t using microalgae
Beuckels A n nelies1, Erik Sm olders2 and Koenraad M uylaert1
1 A quatic Biology, KU Leuven Kulak, Etienne Sabbelaan 53, 8500 K o rtrijk, Belgium
E-mail: [email protected] kuleuven-kortriik.be
2 Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20 bus 2459, 3001 Leuven,
Belgium
The discharge o f secondary effluents fro m wastewater treatm ent, containing nitrogen (N) and
phosphorus (P), can cause a risk o f e utrophication o f surface waters and seas. Microalgae have the
a b ility to remove these nutrients sim ultaneously from wastewater. Besides P is becoming scarce and
N more expensive to produce, which stim ulates the reuse o f both nutrients fro m wastewater. Due to
the depletion o f m ineral phosphate reserves, the recycling o f P w ill be necessary to guarantee the
production o f fe rtiliz e r fo r food production. The produced algal biomass contains valuable lipids,
carbohydrates and proteins th a t can be used as source o f energy, b ulk chem icals and animal feed.
The use o f wastewater n utrients is necessary to make algal biofuel production both sustainable and
econom ically achievable. The objective o f th is research is to id e n tify the bio tic and abiotic
co nditions th a t are o ptim al fo r the removal o f P from wastewaters by m icroalgae.
Wastewaters have a variable N:P ratio therefore we exam ined the effect o f the initia l N:P ratio on
algal grow th, n u trie n t removal and biomass com position. Batch n utrien t uptake experim ents were
perform ed w ith the alga C hlorella vulgaris in synthetic wastewater. This m edium contained various
N (10 to 5 0 m g L ') and P (2 to 10 m g L 1) concentrations. The microalgae com pletely removed 10 to
3 0m gL ' N and 2 to 4 m g L ' P from the m edium . In these treatm ents, the fin al biomass concentration
was up to a fa cto r 2 lower. The biomass m olar N:P ratio ranged fro m 1 5 to 42 indicating th a t more
N is accum ulated, compared to the Redfield ratio o f 16. Therefore com parative batch experim ents
w ith the alga Scenedesmus obliquus, where more P accum ulation is expected, are perform ed.
Real w astew ater also contains P com pounds d iffe re n t from orthophosphate. These inorganic (e.g.
sodium triphosphate, struvite) and organic (e.g. phosphate esters) P com pounds are often not
readily available. Therefore the bio ava ila b ility o f m odel P com pounds is being tested.
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