Abstract
Milk whey processing wastewaters (MWPWs) are characterized by high COD and organic nitrogen content; the concentrations of phosphorus are also relevant. A microalgal-based process was tested at lab scale in order to assess the feasibility of treating MWPW without any dilution or pre-treatment. Different microalgal strains and populations were tested. Based on the obtained results, Scenedesmus acuminatus (SA) and a mixed population (PM) chiefly made of Chlorella, Scenedesmus, and Chlamydomonas spp. were grown in duplicate for 70 days in Plexiglas column photobioreactors (PBRs), fed continuously (2.5 L culture volume, 7 days hydraulic retention time). Nutrient removal, microalgae growth, photosynthetic efficiency, and the composition of microalgal populations in the columns were monitored. At steady state, the microalgal growth was similar for SA and PM. The average removal efficiencies for the main pollutants were: 93% (SA), 94% (PM) for COD; 88% (SA) and 90% (PM) for total N; and 69% (SA) and 73% (PM) for total P. The residual pollution levels in the effluent from the PBRs were low enough to allow their discharge into surface waters; such good results were achieved thanks to the synergy between the microalgae and bacteria in the CO2 and oxygen production/consumption and in the nitrogen mineralization.
Highlights
The dairy industry includes a number of processes, starting from raw milk and generating different products to be used as food, feed, or ingredients in the food industry [1]
The tested wastewater was collected from a factory processing milk whey to recover lactose and casein to be used as animal feed
These are stored in an equalization tank (843 m3 ) and undergo aerobic biological treatment based in a membrane bioreactor
Summary
The dairy industry includes a number of processes, starting from raw milk and generating different products to be used as food, feed, or ingredients in the food industry (pasteurized and sour milk; yoghurt; hard, soft, and cottage cheese; cream and butter products; ice cream; milk and whey powders; lactose; condensed milk; as well as various types of desserts) [1]. In Europe, more than 170.1 million tons of raw milk are produced and 158.6 million tons of milk are delivered to dairies to be processed into fresh products (drinking milk, yoghurts, cream, fermented milks) and manufactured products (cheese, milk powder, butter, whey, etc.) [2]. According to Slavov [1], wastewater production ranges between 0.5 to 37 m3 /m3 of processed milk, with an average of 2.5. Narrower ranges have been indicated: Ahmad et al [5] reported water consumptions between
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