Our customer specialises in processing potatoes for the purpose of manufacturing products such as: potato starch, crystalline and anhydrous glucose, glucose syrups, potato flakes or potato protein for feedstuff purposes. The main objec-tive of the client is to concentrate and recover as much protein and potassium resulting from a protein decanting line, which is part of the so called PPRP: Potato Protein Recovery Plant. The PPRP is a typical installa-tion for the recovery of fodder protein from starch potatoes, based on acid-thermal coagulation of proteins. Hence, the aim was to perform a trial during which the potato wastewater is concentrated as much as possible: have high recovery rate and reduce the amount of concentrate to be disposed of or transported to a biogas plant located within several kilometres from the main site.
In order to study the feasibility of this application, a two months trial was performed on site and 17 process runs and chemical cleanings were carried out by using the same set of AFC99 membranes on a BRO BUF unit.
Most process runs were performed with feed stream starting at 13 mS/cm and concentrated up to 45 mS/cm; meaning a volumetric concentration factor between 3 – 3.5 VCF, operating between 30 – 35 bar and process temperature between 40 – 50°C.
A summary of the feed stream analysis is reported in the table below
Table 1: Potato wastewater feed stream analysis.
Biological pretreatment uses the Activated Sludge Process, which comprises prefiltration, denitrification in a 125m3 stirred tank, and two 125m3 aeration tanks. The tubular ultrafiltration (UF) system recovers the biomass post-nitrification. A 10-fold concentration of biomass is achieved, and the concentrated biomass is recycled to the de-nitrification stage. Approximately 3% of the UF permeate (biologically-pretreated leachate) is recycled to the aeration tanks for foam control.
The UF permeate is concentrated by 2-stage RO. The first stage uses PCI’s tubular membrane system, and achieves a concentration factor of up to 5. The permeate from the first stage is then concentrated in the second stage, which uses PCI’s spirallywound membrane system and achieves a concentration factor of 4. Both stages operate at 40-50 bar as well as ambient temperature, and are chemically cleaned on a weekly basis. The cleaning solution is returned to the biological pretreatment process. The concentrate from the second stage is returned to the first stage.
The installation comprises a 2-effect evaporator which achieves a 10-fold concentration.