In this work valorization of the underexploited industrial solid residue generated after agar extraction from Gelidium sesquipedale was studied by using subcritical water in a semicontinuous fix-bed reactor. First, a complete characterization of this by-product was carried out, determining up to 21% (w/w) of protein content (for a nitrogen factor of 4.9) with high content of essential amino acids, 37% (w/w) of carbohydrate fraction and high amount of ash, 22% (w/w). The effect of temperature, in the range from 129 to 200 °C, and flow rate, in the range from 2 to 6 mL min −1 , on protein and carbon fraction extraction/hydrolysis was studied. At constant flow rate of 2 mL min −1 , a maximum in the protein extraction was achieved at 185 °C. Higher temperatures led to degradation of protein or its hydrolysis products. Free amino acids release followed the same trend as the protein fraction. The most temperature sensitive amino acids, as determined by gas chromatography (EZ:faast Phenomenex), were serine and aspartic and glutamic acids. As a consequence, the selectivity towards non-polar amino acids increased by working at high severity factors. A Pearson correlation between antioxidant capacity of the collected extracts with the bioactive compounds determined in the extracts (total polyphenolic compounds -TPC-, peptides and free amino acids) was established, being stronger for TPC. The ash content in the solid residue after treatment steadily increased with temperature due to non-solubilization being possible its application in agriculture as fertilizers.

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An Anaerobic Membrane Bioreactor (AnMBR) pilot plant was studied to improve certain operational conditions of AnMBRs that treat high oil and grease wastewaters discharged from a snacks factory. A comparison of its performance and behavior was made with an upflow anaerobic reactor throughout the first eight weeks of its operation. Raw snack food wastewater was characterized by oil and grease concentrations of up to 6,000 mg/l, with chemical oxygen demand (COD) and biological oxygen demand (BOD(5)) concentrations of up to 22,000 and 10,300 mg/l, respectively. The AnMBR achieved COD removal efficiencies of 97% at an organic loading rate (OLR) of 5.1 kg COD/m(3) d. The filtration flux, and the suction, backwash and relaxation times for each cycle were all varied: an 11 min filtration time involving 10 s pre-relaxation, 20 s backwash and 70 s post-relaxation was finally selected. The filtration flux for long-term operation was between 6.5 and 8.0 l/m(2) h. The study also tested physical cleaning strategies such as intensive backwashing cycles and extended relaxation mode, and different chemical cleaning methods, such as chemically enhanced backwash on air and chemical cleaning by immersion.

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