Lin S.D. Water and Wastewater Calculations Manual

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Wastewater Engineering 705

(b) Second-stage filter, from Steps 6 and 7

BOD loading rate ⫽ 236.2 kg/d ⫼ 1467 m

⫽ 0.161 kg/(m

⭈ d)

Step 10. Check hydraulic loading rate to each filter

(a) For first-stage filter, recirculation ratio r

⫽ 1.8, and from Step 5

(b) For second-stage filter, r

⫽ 1.8, from Step 8

Formulation for plastic media. Numerous investigations have been under-

taken to predict the performance of plastic media in the trickling filter

process. The Eckenfelder formula (1963) and the Germain (1965) applied

Schulze formulation (1960) are the ones most commonly used to describe

the performance of plastic media packed trickling filters.

Eckenfelder formula. Eckenfelder (1963) and Eckenfelder and Barnhart

(1963) developed an exponential formula based on the rate of waste

removal for a pseudo-first-order reaction, as below:

(6.136)

where S

⫽ effluent soluble BOD

, mg/L

⫽ influent soluble BOD

, mg/L

K ⫽ observed reaction rate constant, m/d or ft/d

⫽ specific surface area

⫽ surface area/volume, m

or ft

/ft

D ⫽ depth of media, m or ft

q ⫽ influent volumetric flow rate

⫽ Q/A

Q ⫽ influent flow, m

/d or ft

A ⫽ cross-sectional area of filter, m

or ft

m, n ⫽ empirical constants based on filter media

5 exp[2KA

11m

D/q

]

5 14.4 m

/sm

HLR 5

s1 1 1.8d 3 3785 m

733.5 m

5 45.2 m

/sm

HLR 5

s1 1 1.8d 3 3785 m

234.5 m

706 Chapter 6

The mean time of contact t of wastewater with the filter media is related

to the filter depth, the hydraulic loading rate, and the nature of the filter

packing. The relationship is expressed as

(6.137)

and

C > 1/D

(6.138)

where t ⫽ mean detention time

C, n ⫽ constants related to the specific surface

and configuration of the packing

Other terms are as in Eq. (6.136).

Eq. (6.136) may be simplified to the following form

⫽ exp[–kD/q

] (6.139)

where k is a new rate constant, per day.

Example: Estimate the effluent soluble BOD

from a 6-m (20-ft) plastic packed

trickling filter with a diameter of 18 m (60 ft). The influent flow is 4540 m

(1.2 Mgal/d) and the influent BOD is 140 mg/L. Assume that the rate constant

k ⫽ 1.95 per day and n ⫽ 0.68.

solution:

Step 1. Calculate the area of the filter A

A ⫽ p(18 m/2)

⫽ 254 m

Step 2. Calculate the hydraulic loading rate q

q ⫽ Q/A ⫽ 4540 m

/d ⫼ 254 m

⫽ 17.9 m

/(m

⭈ d)

⫽ 19.1 (Mgal/d)/acre

Step 3. Calculate the effluent soluble BOD using Eq. (6.139)

5 27 mg/L

5 140 mg/L exp[21.95 3 6/s17.9d

0.68

]

5 S

exp[2kD/q

]

sQ/Ad

Wastewater Engineering 707

Germain formula. In 1966, Germain applied the Schultz (1960) formula-

tion to a plastic media trickling filter and proposed a first-order equation

as follows:

⫽ exp[–k

D/q

] (6.140)

where S

⫽ total BOD

of settled effluent, mg/L

⫽ total BOD

of wastewater applied to filter, mg/L

⫽ treatability constant corresponding to depth of filter

at 20⬚C

D ⫽ depth of filter

q ⫽ hydraulic loading rate, m

/(m

⭈ d) or gal/min/ft

n ⫽ exponent constant of media, usually 0.5

The treatability constant at another depth of the filter must be corrected

for depth when the k

value is determined at one depth. The relation-

ship proposed by Albertson and Davis (1984) is

⫽ k

)

(6.141)

where k

⫽ treatability constant corresponding to depth D

of filter 2

⫽ treatability constant corresponding to depth

of filter 1

⫽ depth of filter 1, ft

⫽ depth of filter 2, ft

x ⫽ 0.5 for vertical and rock media filters

⫽ 0.3 for crossflow plastic media filters

The values of k

and k

are a function of wastewater characteristics, the

depth and configuration of the media, surface area of the filter, dosing

cycle, and hydraulic loading rate. They are interdependent. Germain

(1966) reported that the value of k for a plastic media filter 6.6 m (21.6 ft)

deep, treating domestic wastewater, was 0.24 (L/s)

and that n is 0.5.

This VFC media had a surface area of 88 m

(27 ft

/ft

). The ranges

of k values in (L/s)

0.5

for a 6-m (20-ft) tower trickling filter packed

with plastic media at 20⬚C are 0.18 to 0.27 for domestic wastewater, 0.16

to 0.22 for domestic and food waste, 0.054 to 0.14 for fruit-canning

wastes, 0.081 to 0.14 for meat packing wastes, 0.054 to 0.11 for paper

mill wastes, 0.095 to 0.14 for potato processing, and 0.054 to 0.19 for a

refinery. Multiplying the value in (L/s)

0.5

by 0.37 obtains the value

in (gal/min)

0.5

/ft

Distributor speed. The dosing rate of BOD

is very important for treatment

efficiency. The instantaneous dosing rate is a function of the distributor

708 Chapter 6

speed or the on–off times for a fixed distributor. The rotational speed of

a rotary distributor is expressed as follows:

(6.142)

(6.143)

where n ⫽ rotational speed of distributor, rev/min

⫽ total applied hydraulic loading rate, m

/(m

⭈ d) or

⫽ q ⫹ q

(gal/min)/ft

q ⫽ influent wastewater hydraulic loading rate,

/(m

⭈ d) or (gal/min)/ft

⫽ recycle flow hydraulic loading rate, m

/(m

⭈ d) or

(gal/min)/ft

a ⫽ number of arms in rotary distributor assembly

DR ⫽ dosing rate, cm or in per pass of distributor arm

The required dosing rates in inches per pass for trickling filters is

determined approximately by multiplying the organic loading rate,

expressed in lb BOD

/1000 ft

, by 0.12. For SI units, the dosing rate

in cm per pass can be obtained by multiplying the loading rate in

kg/m

by 0.30.

Example: Design a 8.0 m (26 ft) deep plastic packed trickling filter to treat

domestic wastewater and seasonal (summer) food-process wastewater with

given conditions as follows:

Average year-round domestic flow Q 5590 m

/d (1.48 Mgal/d)

Industrial wastewater flow 4160 m

/d (1.1 Mgal/d)

Influent domestic total BOD

240 mg/L

Influent domestic plus industrial BOD

520 mg/L

Final effluent BOD

ⱕ 24 mg/L

Value of k at 26⬚C and at 6 m 0.27(L/s)

0.5

(from pilot plant study) or 0.10 (gal/min)

0.5

/ft

Sustained low temperature in summer 20⬚C

Sustained low temperature in winter 10⬚C

solution:

Step 1. Compute k value at 20⬚C at 6 m

5 0.22sL/sd

0.5

5 0.27sL/sd

0.5

3 1.035

20226

20@6

5 k

26@6

T226

n 5

1.6q

asDRd

sUS customary unitsd

n 5

0.00044q

asDRd

sSI unitsd

Wastewater Engineering 709

Step 2. Correct the observed k

value for depth of 8 m, using Eq. (6.141)

⫽ k

)

At 8 m depth

Step 3. Compute the summer total flow

Q ⫽ (5590 ⫹ 4160) m

⫽ 9750 m

/d ⫻ 1000 L/m

⫼ 86,400 s/d

⫽ 112.8 L/s

Step 4. Determine the surface area required for an 8-m deep filter for

summer, using Eq. (6.140)

⫽ exp[⫺k

D/q

]

Substituting Q/A for q in Eq. (6.140) and rearranging yields

ln S

⫽⫺k

D/(Q/A)

A ⫽ Q[⫺(ln S

)/k

1/n

⫽ 112.8[⫺(ln 24/520)/(0.19 ⫻ 8)]

1/0.5

⫽ 462 (m

)

Step 5. Similarly, determine the surface area required for an 8-m deep filter

during the winter at 10⬚C to meet the effluent requirements

(a) Determine k

for 6-m filter

10@8

⫽ 0.27 (L/s)

0.5

⫻ 1.035

10 ⫺ 26

⫽ 0.156 (L/s)

0.5

(b) Correct k

value for 8-m filter

10@8

⫽ 0.156 [(L/s)

0.5

] ⫻ (6/8)

0.5

⫽ 0.135 (L/s)

0.5

Q ⫽ 5590 m

/d ⫻ 1000 L/m

⫼ 86,400 s/d

⫽ 64.7 L/s

A ⫽ 64.7[⫺(ln 24/240)/(0.135 ⫻ 8)]

⫽ 294 (m

)

5 0.19sL/sd

0.5

5 0.22sL/sd

0.5

3 0.866

20@8

5 k

20@6

s6/8d

0.5

710 Chapter 6

Step 6. Select the design area required

The required design area is controlled by the summer condition. Because the

area required for the summer condition is larger (see Steps 4 and 5), the

design area required is 462 m

Step 7. Compute the hydraulic loading rates, HLR or q

(a) For summer

HLR ⫽ 9750 m

/d ⫼ 462 m

⫽ 21.1 m

/(m

⭈ d)

⫽ 518 gal/ft

⭈ d

(b) For winter

HLR ⫽ 5590 m

/d ⫼ 462 m

⫽ 12.1 m

/(m

⭈ d)

⫽ 297 gal/ft

⭈ d

Step 8. Check the organic (BOD) loading rates

(a) For summer

(b) For winter

Step 9. Determine rotation speed of rotary distributor, using Eq. (6.142)

The required dosing rates in cm/pass of arm for the trickling filter can be approx-

imately estimated by multiplying the BOD loading rate in kg/(m

⭈ d) by 0.30.

(a) For summer, dose rate DR is, from Step 8a

DR ⫽ 1.37 ⫻ 0.3 ⫽ 0.41 cm/pass

5 22.5 lb/1000 ft

5 0.36 kg/sm

BOD loading 5

5590 m

/d 3 240 g/m

3696 m

3 1000 g/kg

5 85.6 lb/1000 ft

5 1.37 kg/sm

BOD loading 5

9750 m

/d 3 520 g/m

3696 m

3 1000 g/kg

5 3696 m

Volume of filter 5 8 m 3 462 m

Wastewater Engineering 711

Using 2 arms in the rotary distributor, a ⫽ 2; from Step 7a ⫽ 21.1 m

/(m

⭈ d)

or 1 revolution every 88.5 min

(b) For winter

From Step 8b

DR ⫽ 0.36 ⫻ 0.3 ⫽ 0.108

From Step 7b

⫽ 12.1 m

/(m

⭈ d)

Thus

or one revolution every 40 min

23 Rotating Biological Contactor

The use of plastic media to develop the rotating biological contactor

(RBC) was commercialized in Germany in the late 1960s. The process

is a fixed-film (attached growth) either aerobic or anaerobic biological

treatment system for removal of carbonaceous and nitrogenous mate-

rials from domestic and industrial wastewaters. It was very popular

during the late 1970s and early 1980s in the United States.

The RBC process can be used to modify and upgrade existing treat-

ment systems as secondary or tertiary treatment. It has been success-

fully applied to all three steps of biological treatment, that is BOD

removal, nitrification, and denitrification.

The majority of RBC installations in the northern United States

have been designed for removal of BOD

or ammonia nitrogen (NH

-N),

or both, from domestic wastewater. Currently in the United States

there are approximately 600 installations for domestic wastewater

treatment and more than 200 for industrial wastewater treatment.

Over 1000 installations have been used in Europe, especially in

Germany.

5 0.025srev/mind

n 5

0.00044 3 12.1

2 3 0.108

5 0.0113 srev/mind

n 5

0.00044 q

asDRd

0.00044 3 21.1

2s0.41d

712 Chapter 6

Figure 6.28 (A) RBC units, (B) A view of an 84-unit RBCs

for nitrification in Peoria, Illinois.

23.1 Hardware

The basic elements of the RBC system are media, shaft, bearings,

drive, and cover. The RBC hardware consists of a large-diameter and

closely spaced circular plastic media which is mounted on a horizon-

tal shaft (Fig. 6.28). The shaft is supported by bearings and is slowly

rotated by an electric motor. The plastic media are made of corrugated

polyethylene or polystyrene material with various sizes and configu-

rations and with various densities. The configuration designs are based

on increasing stiffness and surface area, serving as spaces providing

a tortuous wastewater flow path and stimulating air turbulence. As an

exception, the Bio-Drum process consists of a drum filled with 38 mm

plastic balls.

Wastewater Engineering 713

The diameters of the media range from 4 ft (1.22 m) to 12 ft (3.66 m),

depending on the treatment capacity. The shaft lengths vary from 5 ft

(1.52 m) to 27 ft (8.23 m), depending on the size of the RBC unit

(Banerji, 1980). Commonly used RBC shafts are generally 25 to 27 ft

(6.62 to 8.23 m) in length with a media diameter of 12 ft (3.66 m).

Standard density media provide 100,000 ft

(9290 m

) of surface area.

About 40% of the media is immersed in the wastewater at any time

in trapezoidal, semicircular, or flat-bottom rectangular tanks with

intermediate partitions in some cases. The shaft rotates at 1.5 to

1.7 rev/min for mechanical drive and 1.0 to 1.3 rev/min for air drive

units (Fig. 6.29). The wastewater flows can be perpendicular to or par-

allel to the shafts.

23.2 Process description

In domestic wastewater treatment, the RBC does not require seeding

to establish the biological growth. After RBC system startup, microor-

ganisms naturally present in the wastewater begin to adhere to the

rotating media surface and propagate until, in about 1 week, the entire

Figure 6.29 Schematic diagram of air-drive RBC.

714 Chapter 6

Figure 6.30 Mechanism for attached growth media in RBC system.

surface area will be covered with an approximately 1- to 4-mm thick

layer of biological mass (biomass). The attached biomass contains about

50,000 to 100,000 mg/L suspended solids (Antonie, 1978). The microor-

ganisms in the film of biomass (biofilm) on the media remove biodegrad-

able organic matter, nitrogen, and dissolved oxygen in wastewater and

convert the pollutants to more benign components (biomass and gaseous

by-products).

In the first-stage RBC biofilm, the most commonly observed fila-

mentous bacterium is Sphaerotilus, Beggiatoa (a sulfur bacterium);

Cladothrix, Nocardia, Oscillatoria, and filamentous fungus, Fusarium,

are also found, though less frequently. Nonfilamentous organisms in the

first stage are Zocloea and Zooglear filipendula, Aerobacter aerogen,

Escherichia coli, unicellular rods, spirilla and spirochaetes, and uni-

cellular algae. The final stages harbor mostly the same forms of biota

in addition to Athrobotrys and Streptomyces reported by investigators

(Pretorius, 1971; Torpey et al., 1971; Pescod and Nair, 1972; Sudo et al.,

1977; Clark et al., 1978; Hitdlebaugh and Miller, 1980; Hoag et al., 1980;

Kinner et al., 1982).

In continuous rotation, the media carry films of wastewater into the

air, which then trickle down through the liquid film surface into the bulk

liquid (Figs. 6.30 and 6.31). They also provide the surface area neces-

sary for absorbing oxygen from air. Intimate contact between the waste-

water and the biomass creates a constantly moving surface area for the

bacteria-substrate-oxygen interface. The renewed liquid layer (waste-

water film) on the biomass is rich in DO. Both substrates and DO