Environmental Technology ChimH409 (2-0-1) Michel Verbanck 2012 Universite Libre de Bruxelles Bruface Dept Water Pollution Control

Course structure Part 1. Introduction (incl. generic methods) Part 2. Air pollution control engineering Part 3. Water & wastewater treatment Part 4. Solid and hazardous wastes

Part 3. Water & wastewater treatment

Trickling Filter

Activated sludge process

external medium bacteria constitutive organic matter waste hydrolysis through exoenzymes

Surface aerators

Submersed porous diffuser

Decoupling of the agitation / mixing function from the aeration provision

Activated sludge flocs Note filamentous bacteria Note Vorticella and other protozoa

The Monod Equation –  = growth rate constant, time-1 –  max = maximum growth rate constant, time-1 –S = substrate concentration in solution –K s = substrate concentration when the growth rate constant is half the maximum rate constant.

Activated sludge model The modeling approach presented here is the classical one, but variants exist. Lawrence, A.W. and McCarty, P.L. (1970) Unified basis for biological treatment design and operation. J. Sanit. Engin. ASCE 96, 757–778.

Biomass budget

It can be shown that, in the case with recycling, exactly the same rule applies, but with substitution of the hydraulic residence time, by the cell residence time. The importance of this formula is that it determines the extent of newly produced sludge. One option is thus to play on the negative term (endogenous decay) to try to minimize the amount of biosolids wastes to be disposed (see Table 15.4)

Based now on the substrate budget, we find It shows that the only two (professional) ways to operate an activated sludge plant are to base on maintaining, either a constant MLSS, or a constant sludge age. This is the so-called Walker rule. if

Sludge Volume Index, SVI SVI = (volume of sludge after 30 min. settling, ml) x 1000 mg/L suspended solids A mixed liquor has 4000 mg/L suspended solids. After 30 minutes of settling in a 1 L cylinder, the sludge occupied 400 ml. SVI = (400 x 1000)/ 4000 = 100 Good settling if SVI 200 …. problems

Bulking sludge, excessive development of filamentous bacteria, poor settleability of the flocs.

submerged membrane modules (Kubota ®) 0.4 µm porosity allows improved separation of newly produced biosolids from final treated effluent (even if activated sludge flocs have a poor settling behaviour, chronic or episodic)

Anammox (ANaerobic AMMonium OXidation) Recent evolution of biological wastewater treatment processes