Combining submerged membrane technology with anaerobic and ...

Materials and methods2.1.4. Other control parameters2.1.4.1. pHThe pH is one of the key parameters measured in wastewater treatment systems,since its control is important to maintain the biological activity of the microorganismsinvolved in the treatment process. The pH measurements were performed with differentelectrodes (Crison Instruments, S.A., 52-03). The sensibility of the instrument is ± 1 mV,corresponding to 0.01 pH units. The electrodes are calibrated at room temperature withtwo standard buffer solutions of pH 7.02 and 4.00.2.1.4.2. Dissolved oxygenDifferent dissolved oxygen probes (AQUALITYC, model OXI-921 and WTW, modelOXY-3401) connected to a meter (M-Design Instruments TM-3659) was used to controlDO concentration in the reactor.2.1.4.3. TemperatureThe oxygen probes previously mentioned were equipped with a thermo par thatallowed to measure temperature.2.1.4.4. Alkalinity and alkalinity ratioAlkalinity of water is its acids-neutralization capacity it is the sum of all the titratablebases and its value may vary significantly with the end-point pH used. Alkalinity issignificant in many uses and treatments of natural waters and wastewaters. Because thealkalinity of many surface waters is primarily a function of carbonate, bicarbonate andhydroxide content, it is taken as an indication of the concentration of these constituents.The measured values may include contributions from borates, phosphates, silicates, orother bases. Alkalinity measurements are used in the interpretation and control of waterand wastewater treatment process, such as anaerobic digestion. A typical symptom of theabnormal operation of an anaerobic reactor is the increase of the organic acidsconcentration, which occurs when their production exceeds their consumption.Total alkalinity (TA) can be considered, approximately, as a sum of the alkalinity dueto the presence of bicarbonate and volatile fatty acids (VFA), expressed as mg·L -1equivalent of CaCO 3. Partial alkalinity (PA), measured by the titration till pH 5.75,corresponds to the alkalinity of bicarbonate (Jenkins et al., 1983), while the intermediate73