Biological Wastewater Treatment, Revised and Expanded

of wastewater treatment is to remove pollutants that can harm the if they are discharged into it. Because of the deleterious effects of low dissolved oxygen (DO) concentrations on aquatic life, wastewater treatment of pollutants that would deplete the

of biochemical operations, it is necessary to of what wastewater treatment engineers hope to accomplish if we are to develop the capability for their design,

biochemical operations is depicted in Figure 2.3. Before insoluble organic materials can be consumed, they must be solubilized, just as was necessary in aerobic systems. Furthermore, large soluble organic molecules must be reduced in size to facilitate transport across the cell membrane. The reactions responsible for solubilization and size reduction are usually hydrolytic and are catalyzed by extracellular enzymes

of reactants of one reactant

(3.13) of half-reactions, McCartyhas de-

0.207 = 0.50 20 mg/L 0.20 K= 40 mg/L 0: 0.15

III state, and thus those electrons are incorporated into the biomass even though they will not be measured in the COD test. This is because nitrogen does not accept or give up electrons in the COD test. Consequently, if biomass is represented by CHON, its COD must be multiplied by 1.4 for the balance to work, as suggested by Eq. 3.17. Thus, to generalize: COD removed = 0 equivalents of terminal electron acceptor used

on the effects of temperature on the hydrolysis of particulate substrate. it is an enzymatic step, the hydrolysis coefficient, kh, is likely to of experimental data to sim- of temperature on of the effects of temperature on other processes, such as phosphorus

provided per mg of COD removed for each of the following situations? What quantities of micronutrients will be required? Do not derive the stoichiometric equations. Rather, answer the question using generaliza- tions presented in the text. 0.70 mg biomass COD formed/mg substrate COD removed.

we saw that many types of biochemical operations are used in waste- be a difficult task if we of com- of events occur within them,

of A in the influent and effluent (or reactor), respec- Chas been used here to emphasize the of its state, i.e., soluble or particulate. For the systems with which we deal it is safe

Fw •Ss,Xa,H•Xo biomass separator

(5.22) Rearrangement gives: X = f ·b •@ ·X = (®c) [fo·bH·@c·YH(Sso - Ss)] H c T l (5.23) The units of Xwill be the same as the units of Xs,H• Debris adds to the total suspended solids concentration in the bioreactor, but does not add to the degradative (5.25) + bH·T The active fraction of the biomass, is defined as the concentration of active biomass divided by the total biomass concentration. Division of Eq. 5.19 by Eq. 5.24 and rearrangement yields: + fo·bH·@c

Tank In Chapter 5, we investigated the growth of aerobic heterotrophic bacteria in a single continuous stirred tank reactor (CSTR) receiving a soluble substrate. Through de- velopment of a simple model we saw that the SRT is an important determinant of

specific growth rate is controlled by the soluble substrate concentration, as expressed by the Monad equation (Eq. 3.36). Since the soluble substrate concentration is var- ying over time, so is the specific growth rate. This means that the bacteria are in a continually changing state. For the reactor configuration in Figure 5.1, the SRT is determined solely by the reactor volume and the wastage flow rate. Consequently,

(6.2) where represents the ammonia-N concentration in the feed that is available to the nitrifiers, i.e., the amount remaining after consideration of the amount used by the heterotrophs for biomass synthesis. fis 0.20, the destruction of 100 g of biomass COD will lead to the release of 20 g of biomass debris COD and the consumption of 80 g of oxygen. As reflected by and iNixo, the nitrogen contents of biomass and biomass debris are around 0.086 and 0.06 g N/g biomass COD, respectively. Consequently, destruction of 100 g of biomass will also lead to the release of 7.4 g of ammonia- (100[0.086-(0.20 · 0.06)]), which can act as substrate for autotrophic bacteria.

of microbial cultures in single contin- of solids reten- of some industrial wastewaters, more

_,,--

of Part II, we have examined models for characterizing of ideal suspended growth bioreactors. Before those models can be of wastewater treatment systems, however, values

Growth of this book addresses the technical aspects of the design and evaluation of of designing and evaluating such operations, with

bacteria, which are not capable of accumulating phosphorus. Consequently, the lower limit on the SRT for phosphorus removal is generally higher than that for soluble substrate removal. On the other hand, the lower limit on the SRT for phosphorus removal is similar to the lower limit for nitrification, suggesting that it may be difficult to operate a bioreactor for phosphorus removal without experiencing the

of bioreactor configurations for the of removing soluble organic matter. It is a flexible, reliable process capable of producing a high quality effluent. Soluble organic matter is reduced to low levels,

if the wastewater contains a high of colloidal organic matter that can be removed by entrapment in the

of biomass and the total oxygen requirement in the various alternative activated of Chapter 5 as modified in Section of flows or volumes into

Ss)] = + + of XM,r V, no term is included of the autotrophic bacteria. If their contribution to the waste

= ll,=

Biological nutrient removal (BNR) processes are modifications of the activated sludge process that incorporate anoxic and/or anaerobic zones to provide nitrogen and/or phosphorus removal. Many variants have been developed, representing a wide range of nutrient removal capabilities. This chapter presents the basic design and operational principles for several of them. It builds upon the theoretical concepts

0]. The process designer must be of these potential impacts and balance the requirements of the liquid and solids 11.2.3 Composition of Organic Matter in Wastewater of the organic matter present in a wastewater, particularly its bio- of BNR processes. In the anaerobic zone,

of aerobic bioreactors to stabilize par- of waste- of a relatively

of hydrolysis of particulate substrate under anoxic con- of this model also indicates that the overall stabilization of organic matter in the A/A D process will be the same as achieved in a CAD system

The term anaerobic process refers to a diverse array of biological wastewater treat- ment systems from which dissolved oxygen and nitrate-N are excluded. In most instances they are operated to convert biodegradable organic matter, both soluble and particulate, to methane and carbon dioxide. Since methane is a sparingly soluble gas, most is evolved and recovered, thereby removing organic matter from the liquid

of suspended growth biochemical opera-

of microorganisms. However, as discussed in Section 1.2.3, attached growth

of the flux into a steady-state biofilm associated with a given ln(l + S[,)]} = st, + kl, are calculated with + 0.0017 + 0.0017)

Packed Towers of attached growth bioreactors were listed in Table 1.2. Among those,

0 100 200 300 400 500 600 Cross Sectional Area, cm

Rotating Disc of attached growth bioreactor is the rotating disc or touching the liquid surface in a long narrow tank. The shaft

Aerated ---W=/' ------- ------

· Ssb ) of substrate by the RDR and they must be solved simultaneously. For a given set of of the bioreactor. The only

of fixed media bioreactors in which the media stays in one position of the hydraulic

Superficial Velocity

of the characteristic film thickness, Lfc:

Applications: Attached Growth Reactors of ideal attached growth reactors and of a

of attached growth biochemical opera- of the wastewater is accomplished by microorganisms growing attached of which there are several types. Trickling filters are aerobic and are

of a coupled TF/AS system. Unfortunately this cannot of substrate rather than on the growth of biomass. Thus, while of the suspended of heterotrophic biomass, cell debris, inert influent

of aerobic attached of one to two revolutions per minute to alternately expose

of wastewaters of trickling filters and rotating biological of new

120m 12()

of biogenic organic matter, nitrification, and deni- of biological phos-

Acronyms

Symbols

Unit Conversions