Miguel Minhalma

Tannic-membrane interactions on ultrafiltration of cork processing wastewaters

Abstract Cork processing wastewaters are very complex mixtures of vegetal extracts and have, among other natural compounds, a very high content of phenolic/tannic colloidal matter, that is responsible for severe problems of membrane fouling and drastic flux decline. In the present work the identification and quantification of phenolic/tannic compounds, responsible for membrane fouling, is carried out through the use of reverse phase high pressure liquid chromatography (HPLC). The compounds studied were gallic acid, protocatechuic acid, vanillic acid, syringic acid, ferulic acid and ellagic acid. The very different characteristics of these compounds in terms of hydrophilicity/hydrophobicity were correlated to their rejection coefficients for two cellulose acetate ultrafiltration membranes of 6000- and 98000-Da molecular weight cut-off (MWCO). The ultrafiltration transmembrane pressures ranged from 0.5 to 4 bar and the feed flowrate from 100 to 200 l/h. The more hydrophobic component (the ellagic acid) is almost totally retained and that independently of the membrane MWCO, transmembrane pressure, and feed flowrate leading to the conclusion of formation of an adsorption layer responsible for membrane fouling.

Cork industry wastewater partition by ultra/nanofiltration: A biodegradation and valorisation study

Wastewater from cork processing industry present high levels of organic and phenolic compounds, such as tannins, with a low biodegradability and a significant toxicity. These compounds are not readily removed by conventional municipal wastewater treatment, which is largely based on primary sedimentation followed by biological treatment. The purpose of this work is to study the biodegradability of different cork wastewater fractions, obtained through membrane separation, in order to assess its potential for biological treatment and having in view its valorisation through tannins recovery, which could be applied in other industries. Various ultrafiltration and nanofiltration membranes where used, with molecular weight cut-offs (MWCO) ranging from 0.125 to 91 kDa. The wastewater and the different permeated fractions were analyzed in terms of Total Organic Carbon (TOC), Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), Total Phenols (TP), Tannins, Color, pH and Conductivity. Results for the wastewater shown that it is characterized by a high organic content (670.5-1056.8 mg TOC/L, 2285-2604 mg COD/L, 1000-1225 mg BOD/L), a relatively low biodegradability (0.35-0.38 for BOD(5)/COD and 0.44-0.47 for BOD(20)/COD) and a high content of phenols (360-410 mg tannic acid/L) and tannins (250-270 mg tannic acid/L). The results for the wastewater fractions shown a general decrease on the pollutant content of permeates, and an increase of its biodegradability, with the decrease of the membrane MWCO applied. Particularly, the permeated fraction from the membrane MWCO of 3.8 kDa, presented a favourable index of biodegradability (0.8) and a minimized phenols toxicity that enables it to undergo a biological treatment and so, to be treated in a municipal wastewater treatment plant. Also, within the perspective of valorisation, the rejected fraction obtained through this membrane MWCO may have a significant potential for tannins recovery. Permeated fractions from membranes with MWCO lower than 3.8 kDa, presented a particularly significant decline of organic matter and phenols, enabling this permeates to be reused in the cork processing and so, representing an interesting perspective of zero discharge for the cork industry, with evident environmental and economic advantages.

Development of nanofiltration/steam stripping sequence for coke plant wastewater treatment☆

The present work proposes the optimisation of an integrated process that consists in the coupling of Nanofiltration (NF) with Steam Stripping for the treatment of ammoniacal wastewaters contaminated by cyanides ions and phenols. These wastewaters are fractionated by NF into an ammonium concentrate and an ion-containing permeate stream. The concentrates are further fractionated in the steam stripping column. The NF experiments were performed with a DSS plate and frame Lab-Unit 20, equipped with a HR-98-PP membrane. The NF experiments were run in concentration mode to optimise the concentrate ammonium content/permeate flux as a function of water recovery ratio (RR). The optimisation of the NF/steam stripping integrated process was carried out with a sequential process simulator. The optimisation study showed that the NF should work at a recovery ratio of 40%. At this RR the ammonium can be efficiently concentrated and purified from cyanides at reasonable permeate flowrates. The column steam consumption was also optimised as a function of the NF concentrates flowrate. The integrated process leads to an increase of the stripping efficiency and to significant energy savings (0.698 EURO/m3 treated water).