Water 2 Chem 2020 Spring 2011
Henry’s Law for Dissolved Oxygen Where [O2] is the equilibrium concentration of oxygen in water (mol/L) [O2] = KHPO2 KH is O2’s Henry’s law constant = 1.28 x 10-3 mol/L-atm (25oC) PO2 = (1.00 atm – 0.0313 atm ) (0.2095) = 0.203 atm [O2] = KHPO2 = (1.28 x 10-3 mol/L-atm) (0.203 atm) [O2] = 2.60 x 10-4 mol/L [O2] = (2.60 x 10-4 mol/L) (32 g/mol) = 8.3 mg/L = 8.3 ppm
Figure 8.2 The solubility of oxygen in water at different temperatures and altitudes.
B. O. D. – Biological Oxygen Demand • The method consists of filling with sample, to overflowing, an airtight bottle of the specified size and incubating it at the specified temperature for 5 d. Dissolved oxygen is measured initially and after incubation, and the BOD is computed from the difference between initial and final DO. Because the initial DO is determined shortly after the dilution is made, all oxygen uptake occurring after this measurement is included in the BOD measurement.
BOD is proportional to the concentration of biodegradable carbon constituents in waste water.
A vinegar manufacturer generates a waste stream containing essentially pure acetic acid, C2H4O2, at a concentration of 120 mg·L-1. The waste has a 5-day CBOD of 50 mg·L-1 and a CBOD reaction rate coefficient of 0.1 d-1. a. Determine the theoretical oxygen demand of the waste.
TSS – Total Suspended Solids • TSS of a water sample is determined by pouring a carefully measured volume of water (typically one liter; but less if the particulate density is high, or as much as two or three liters for very clean water) through a pre-weighed filter of a specified pore size, then weighing the filter again after drying to remove all water
Figure 8.3 If organic wastes are discharged into a river, the level of dissolved oxygen in the water falls, and aquatic organisms begin to die.
Figure 8.8 The main steps in the processes used for sewage treatment. Adapted from B.J. Nebel. Environmental Science: The Way the World Works, Third edition. Englewood Cliffs, NJ: Prentice Hall, 1990.
Primary Treatment • Screen • Grit Chamber • Sedimentation Tank • Raw Sewage Sludge
Secondary Treatment aerobic bacteria Waste + O2 CO2 + H2O 90 % of organic material removed by primary and Secondary treatment
Cl2 + H2O HOCl + H+ + Cl- HOCl OCl- + H+ pKa = 7.6 Chlorination
Ecological Engineering “The inventory of species of the earth is really an immense bin of parts available to the ecological engineer. A species evolved to play one role may be used for a different purpose in a different kind of network as long as its maintenance flows are satisfied.” – H. T. Odum Ecological engineers participate in ecosystem design by providing choices of initial species as well as the starting conditions; nature does the rest". It must protect natural ecosystems from alien organisms contained in living technologies. Our practice has been to use either organisms prevalent in the region, or species which cannot survive beyond the confines of the given mesocosm.