Full-Scale Evaluation of Aerated Grit Chambers

Full-Scale Evaluation of Aerated Grit ChambersAuthor(s): Liliana Morales and Debra ReinhartSource: Journal (Water Pollution Control Federation), Vol. 56, No. 4 (Apr., 1984), pp. 337-343Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25042244 .Accessed: 08/04/2014 15:00

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il

Full-scale evaluation of aerated

grit chambers Liliana Morales, Debra Reinhart

The importance of grit removal in wastewater treatment has long been recognized by plant operators and designers. Inad equate grit removal can result in unnecessary abrasion and wear

of mechanical equipment, deposition of grit in pipes or channels, and accumulation of grit in anaerobic digesters and aeration basins. Poor grit chamber operation also creates nuisance con

ditions as a result of the removal of grit with high organic content. Present design criteria for aerated grit chambers call for a

95% removal of 65-mesh grit (particles with diameter equal to 0.210 mm). Because it is difficult to measure grit removal, this information is of little value to treatment plant operators in evaluating grit chamber performance. This investigation eval

uated the performance and design of five full-scale aerated grit chambers in Atlanta. Based on the results, the design which produced the best performance was identified. The effect of operational parameters and physical appurtenances on grit chamber performance was also evaluated.

BACKGROUND In an aerated grit chamber air creates a spiral flow pattern

through the chamber. The spiral velocity is controlled by the quantity of air supplied. This spiral or roll velocity controls the quantity and quality of grit removed. Because grit removal is controlled by roll velocity instead of flow-through velocity, grit removal efficiency can be maintained over the entire design flow range.1

Most aerated grit chambers are designed to remove particles 0.2 mm or larger with specific gravities of approximately 2.65. Adequate detention times for the removal of these particles range between 2 and 5 minutes.2"4 However, if removal of smaller

particles is desired, or if the tank is also for preaeration, longer detention times may be required.3

The effective removal of particles in aerated grit chambers depends on adequate hydraulic control to minimize short-cir

cuiting.5 Short-circuiting can be controlled by appropriate tank geometry and by the relative positions of the inlet port and outlet weirs.6 The placement of longitudinal or transverse baffles with respect to flow may also be a factor in preventing short

circuiting. It has been suggested that long narrow aerated grit chambers

provide better removal than square ones.1 However, no quan

titative evidence is available to support this contention.

The quality of grit removed is also affected by the type of equipment used. Some of the most commonly used devices are

the air lift pump, tubular conveyor, water jet pump, chain and

bucket, screw conveyor and grit pump.6 In this study, the effectiveness of grit removal equipment,

tank geometry, baffling and air flow rates was investigated.

METHODOLOGY A detailed evaluation of five grit chamber designs in operation

at wastewater treatment facilities in Atlanta was conducted.

Each facility has one or more aerated grit chamber units, each

with unique configuration and equipment. An initial survey of each grit chamber was made to obtain engineering drawings,

modifications to the original design, operator experience with the units and any evidence from throughout the plant of poor grit chamber performance. Each tank was drained to observe

areas of grit deposition which indicated areas of low or no velocity and thus provided a key to the effectiveness of the air source to maintain a uniform roll of wastewater throughout the tank.

In addition, velocity measurements were made throughout the

tanks using a portable water current meter.

Tracer studies were conducted at each plant to evaluate tank

hydraulics. A fluorescent dye was introduced at a point of com

plete mix ahead of the grit chamber inlet. A submersible pump in the effluent channel continuously fed a sample to a fluorom

eter. Dye fluorescence was recorded to produce a curve of flu

orescence versus time. The average detention time for each tank

was obtained from the curve. Flow pattern of the dye through the grit chambers was observed for evidence of short-circuiting and dead zones.

The shape of the grit chamber is not the only key to

good design; diffuser placement, air source, and

adequate baffling all affect performance.

Average values for the quantity and quality of the grit removed

at each plant were obtained from plant records. These values

were compared to the results of samples collected during this

study. The last step in the evaluation of the grit chamber performance

was to measure the percent removal of grit particles equal to

or larger than 65-mesh. Sampling of grit chamber influent and effluent was not feasible because of stratification of grit with

depth in the influent and effluent channels, and the extremely large quantity of sample needed. Instead a more convenient

method was developed to obtain similar results.

It was assumed that all grit equal to or larger than 65-mesh

coming into the plant would be removed in the grit chamber, or would settle in the primary clarifiers. Twenty-four hour com

posited grit samples were collected from the grit hopper and

sludge from the primary clarifiers. Residue analyses were per

formed on these samples (volatile and fixed matter in nonfiltrable residue and in solid and semi-solid samples) by method 209G

April 1984 337


Morales & Reinhart

LONGITUDINAL SECTION

1111

PERFORATEp PIPE

=a

CROSS-SECTION

INLET

Figure 1?R. M. Clayton grit chamber.

in "Standard Methods." The particle size distribution of the

sample inerts was obtained by sieving each ignited sample

through selected U. S. Standard Sieves using a Standard Me

chanical Sieve Shaker. The quantity of grit and raw sludge re

moved during the sampling period and the volume of wastewater

treated were also recorded.

Equations 1 through 5 describe the procedure for calculation

of the percent removal of inerts equal to or larger than 65-mesh across the grit chamber.

X = Q?TSg)(\ - TVSg) XVxXSg (1) where:

X = dry weight of inerts removed over a 24-hour period,

(kg/d), Qg

= wet volume of grit removed over the 24-hour period,

m3/d,

TSg = total solids present in 24-hour composite grit sample,

fraction,

TVSg = total volatile solids present in 24-hour composite grit

sample, fraction,

Vi =

specific weight of water, 1000 kg/m3, and

Sg =

specific gravity of grit inerts, 2.5.

Y= Q5(TSs)(l - TVSS) XVXXSS (2) where:

Y = dry weight of inerts removed by the primary clarifier over a 24 hour period, kg/d,

Qs = wet volume of primary sludge removed over the 24 hour period, m3/d,

TSS = total solids present in 24-hour composite primary

sludge sample, fraction,

TVSS = total volatile solids present in 24-hour composite pri

mary sludge sample, fraction, and

Figure 2?Utoy Creek grit chamber.

Ss =

specific gravity of primary sludge inerts, 1.4.

A = Pa?X) + Pas(Y) (3)

where:

A = dry weight of inerts larger than size "a" present in

the plant influent, kg/d, Pag

= fraction of 24-hour composite grit sample corre

sponding to size "a" (obtained from sieve analysis), and

Pas = fraction of 24-hour composite primary sludge sample

corresponding to size "a" (obtained from sieve anal

ysis). PRa = [PaJLX)/A] X 100 (4)

where:

PRa =

percent removal of influent inerts of size "a" across

the grit chamber.

The percent removal of inerts equal to or larger than 65-mesh

across the grit chamber was calculated as:

PR = (p**+J>i?+V

_Process Design

Figure 4?South River grit chamber.

Three different tank geometries and air flow patterns were studied. The R. M. Clayton grit chamber (Figure 1) has a long narrow configuration, unlike the other four tanks evaluated.

The Utoy Creek (Figure 2) and Flint River (Figure 5) grit cham bers have a square configuration with air fed at the tank center.

However relative inlet/outlet positioning and grit removal equipment differ. The Intrenchment Creek (Figure 3) and South

River (Figure 4) grit chambers also have similar tank geometry but different air positioning, inlet/outlet arrangement, and grit removal equipment. As a result of the similarities and differences among the grit chambers evaluated, it was possible to examine

the effectiveness of particular aspects of each design such as

type of grit removal equipment, baffling for hydraulic control, type of aeration device, and grit washing.

Adequate equipment to control air flow rate was not available

at any of the facilities evaluated so air flow rates could not be optimized. In plants with multiple units it could not be deter

mined if the air was evenly distributed among the tanks.

RESULTS AND DISCUSSION Analysis of tracer studies. The output tracer response curves

are presented in Figures 6 through 10. A summary of the pa rameters developed from the tracer studies is presented in Table 2. Theoretical calculations of detention times and overflow rates

were made using the actual flow rate at the time of the study

AIR ?

SUPPLY

Figure 5?Flint River grit chamber.

and the tank volume. Actual detention times were obtained by measuring the center area of the fluorescence-time curves. The

velocities reported in Table 2 represent the range of velocities measured in a horizontal plane and in the direction of wastewater

roll.

The R. M. Clayton grit chamber has the only long-narrow configuration among those evaluated. Under ideal hydraulic conditions, flow through this type of reactor should be plug flow, that is, the fluid particles pass through the tank and are discharged in the same sequence in which they enter. The par ticles remain in the tank for a time equal to the theoretical detention time. Ideally, if a tracer slug was injected into such a tank to produce a given influent concentration, the trace would

appear in the effluent at that same concentration in a time lapse

equal to the theoretical detention time. The tracer curve would

be represented by a vertical response located at a time equal to

the detention time and approaching zero width.

The R. M. Clayton tracer response curve illustrated in Figure 6 indicates that some longitudinal dispersion of the dye occurred and resulted in a deviation from the ideal plug-flow pattern described above. Actual detention time based on centroid of the curve was 4.6 minutes, which is higher than the theoretical value of 3.7 minutes. This could have been the result of the

Table 1?Summary of grit chambers design features.

Feature R.M. Clayton Utoy Creek Intrenchment Creek South River Flint River

Tank dimensions, m

Width Length Side water depth

Inlet baffle

Effluent baffle

Aeration device

Air header placement

Grit removal

equipment

Grit elevator type

Grit washing provided

3.7 27.2

4.0

no

no

perforated pipe

lateral, perpendicular to flow

chain and bucket

screw conveyor

no

7.6 7.6 3.4

no

yes

discfusers

center

grit pump

screw conveyor

yes

5.5 6.0 2.3

no

yes

discfusers

lateral, parallel to flow

tubular conveyor

tubular conveyor

no

5.5

4.3 2.9

yes

yes

discfusers

lateral, perpendicular to flow

chain and bucket

chain and bucket

no

8.5 8.5 3.7

yes

yes

air lift pump

center

air lift pump

screw conveyor

yes

April 1984 339


Morales & Reinhart

Table 2?Data collected during tracer studies.

Parameter R.M. Clayton Utoy Creek Intrenchment Creek South River Flint River

Theoretical hydraulic detention time, minutes 3.7 7.4 5.0 2.9 35.0

Actual hydraulic detention

time, minutes 4.6 3.8 3.6 5.6 7.8 Overflow rate, m3/m2d 1 409 782 809 1 455 187 Roll velocities, m/s

Surface 0.21-0.61 0-0.61 0-0.54 0.24-0.61 0.09-0.67 Bottom 0.03-0.24 0.03-0.24 0-0.40 0.15-0.36 0.03-0.15

presence of stagnant zones in the tank that delayed dye bleed to the effluent, settling and resuspension of organic particles that adsorbed dye, or the dissolution of initially undissolved dye particles with time. The peak of the curve, which may better represent actual detention time in this case, was 3.5 minutes,

indicating little short-circuiting. The Utoy Creek grit chamber was designed as a complete

mix reactor. Complete mixing in such a tank would ideally produce an output tracer response curve with maximum dye concentration occurring as soon as the dye was introduced. This

concentration would decrease gradually in an exponential func

tion. As shown in Figure 7, this was not the case. Instead, the

tracer response curve represents a condition of arbitrary flow, that is, a flow regime somewhere between plug flow and complete

mix. Uneven dye dispersion and dead spaces were observed,

indicating severe short-circuiting. These observations were ver

ified with the actual detention time of 3.8 minutes obtained from the curve, which was significantly lower than the theoretical

detention time of 7.4 minutes. Short circuiting was caused, in

part, by surges in air flow to the grit chamber.

Results of tracer studies at the Intrenchment Creek grit cham

ber are presented in Figures 8a and 8b, conducted with and

without aeration, respectively. Normal operating procedure did not include aeration because plant personnel claimed that no

improvement in grit removal could be found when the aeration was used. The dye dispersion pattern was basically the same

during both studies. Short circuiting was observed and verified by the curve peak and its relative magnitude with respect to

the rest of the curve. Detention times derived from the tracer

curves were 2.2 and 3.6 minutes for the test with and without

air, respectively. In both cases, the actual detention times were

lOOn

5 10 15 TIME, MIN.

Figure 6?R. M. Clayton tracer curve.

significantly shorter than the theoretical value of 5.0 minutes.

It was clear during the tracer studies that surface velocities through the tank were increased by air input. Because of the relative inlet/outlet positions, this air input encouraged short circuiting through the tank.

The South River grit chamber design is similar to that at Intrenchment Creek except in the position of the air header in relation to the inlet, and the addition of an influent turning baffle. However the results obtained from the tracer studies

(Figure 9a) were very different from those obtained at Intrench ment Creek. The curve represents a condition of arbitrary flow

where mixing seems to be fairly uniform throughout the tank.

The actual detention time obtained from this curve was 5.6

minutes. This value, as for the R. M. Clayton grit chamber, was higher than the theoretical detention time of 2.9 minutes.

A second tracer study was performed at the South River

facility, this time without air (Figure 9b). The blowers were turned off 24 hours before testing and during tracer tests. With air, the only major difference between South River and In trenchment Creek grit chambers was the influent baffle. The results indicated whether a baffle at Intrenchment Creek would improve performance or whether the air header position needed

to be changed. The output tracer response curve is presented in Figure 9b. The curve has a shape similar to that at Intrench

ment Creek with the air on (Figure 8a). An actual detention time of 1.4 minutes was calculated, suggesting that the air header

position was the critical factor. Moving this header to create a

wastewater roll perpendicular to the flow-through length of the tank should improve performance. Although not crucial, the

addition of an influent baffle to encourage the spiral roll should also help reduce short-circuiting.

- IOOt a w 1 1 i ?J I

q: uj - \ o o - \ -I UJ - i \

O-Ll-.-1-r 5 10 15 TIME, MIN.

Figure 7?Utoy Creek tracer curve.

340 Journal WPCF, Volume 56, Number 4


Process Design

100-, LU

o 2 LU

LU2 o: tu oo D^ -1LU U_CL

m

5 10 15 TIME, MIN.

100

LU u 2 LU

or lu

IJLU U_CL

HI

5 10 15 TIME, MIN.

20

Figure 8?Intrenchment Creek tracer curves.

The tracer response curve for the Flint River grit chamber

is presented in Figure 10. The shape of the curve indicates very good mixing throughout the tank. The flow pattern differs sig nificantly from that at Utoy Creek, although the designs are very similar. Differences are attributed to an influent baffle at

Flint River which directs the wastewater to the center of the tank, and into the air induced pumping zone. However, even

with the baffle, short circuiting was severe, as indicated by an actual detention time of 7.8 minutes versus a theoretical de

tention time of 35 minutes. Poor velocity control in the tank was also evident when the tank was drained and accumulations

of grit ranging from 0.15 to 1.5 m (6 in to 5 ft) in depth were found all over the tank bottom.

Percent removal of 65-mesh grit. A summary of the results

of the grit removal studies is presented in Table 3. A 95% removal of 65-mesh grit was achieved at three of the five plants and is thus a valid design criterion. However it is not a practical pa rameter for performance evaluation in the field.

Data in Table 3 indicate that the Flint River grit chamber has the best removal efficiency. However this grit chamber was

operated at overflow rates much lower than typical values of

1 426 m3/m2 d (35 000 gal/day sq ft). Large accumulations of grit in the tank bottom are evidence of the failure of the Flint River design to establish a desirable flow pattern throughout the tank; short circuiting is the apparent result. Under loading conditions comparable to those at the R. M. Clayton and South

River installations, the Flint River grit removal efficiency would no doubt be much lower, perhaps approaching that found at

Utoy Creek.

The Intrenchment Creek grit chamber also removed a high percentage of the incoming grit at an intermediate overflow rate

I0O-1 y* LU / \ / \ 2 \ LU V

LU2 \ (ELU \ -J?J l LLO. \

0-u-,-,-^-r 5 10 15 20 TIME, MIN.

Figure 9?South River tracer curves.

of 809 m3/m2'd (19 860 gal/day-sq ft) However significant short circuiting occurred. Grit accumulations ranged from 0.30

to 0.76 m (1 to 2.5 ft) in depth, which indicates poor hydraulic control. In order to compare these results with those from the

South River and R. M. Clayton facilities at higher overflow rates, grit removal quantities were measured at an overflow rate

of 1 572 m3/m2-d (38 580 gal/day-sq ft). A 62% reduction in the quantity of grit removed was the result. This indicates that at more typical operating conditions the negative effects of short circuiting and inadequate inlet/outlet arrangements would be

more apparent. As previously discussed, the flow pattern at the South River

grit chamber when operated without air was very similar to that

at Intrenchment Creek. Grit removal efficiency at the South River grit chamber with the air off was 82.7%, a lower removal

than the 94.8% during normal operating conditions. This also suggested that performance would decrease significantly at In

trenchment Creek under higher loading conditions. Therefore, Intrenchment Creek was eliminated as an optimum design.

For typical detention times and overflow rates, grit removal

at the R. M. Clayton grit chamber (long, narrow configuration) seemed to be the best among the grit chambers evaluated, both in terms of process efficiency and grit quality. The unit did not

have any unusual operational problems, and the absence of grit

deposits in the tank bottom indicated good spiral roll of the wastewater.

The South River grit chamber achieved a removal of 94.8% during the sampling period. However the grit quality was very poor because of high volatility and moisture content, as seen

in Table 3. This resulted in disposal problems, including bad odors, poor aesthetics around the grit collection area, and in

lOO-i

?J o z ?J

?J2 C?UJ

ZJUJ U-?L

5 10 15 TIME, MIN.

~20

April 1984 341


Morales & Reinhart

- IOOt ^-> LU / \ O / \ 2 - / \ Ui / \ %? ' l \ UJ2 } \ oruj I 1 oo . / I "DOC \

U"Q" / \ 0-1?i-,-,-r-^-, 5 10 15 20

TIME, MIN.

Figure 10?Flint River tracer curve.

creased trips to the landfill. The poor grit quality was related to the type and arrangement of grit removal equipment rather than tank configuration.

Effect of operational parameters on performance. Velocities were measured in all grit chambers to determine actual flow patterns in the tanks and the effect of changes in velocity on performance. As shown in Table 2, a wide range in velocity was found at each facility, but there were no significant variations from one plant to another. The velocity changes did not seem

to affect the overall performance of the units. However areas

of low or zero velocity caused grit deposition in the tanks. Equalization of air flow rates among parallel tanks was not

possible because there were no air flow meters at the grit cham

bers in any of the plants. Air flow rates were manually adjusted in response to velocity measurements so that parallel tanks had

approximately the same roll velocities. This procedure required significant effort and could not easily be performed by the op erators. Unequal air distribution seemed to result in different degrees of removal among the various operating tanks, which

would in the long run cause grit accumulation in subsequent treatment units.

The overflow rate data presented in Table 2 and the percent removal data in Table 3 show that overflow rate is not crucial to good removal, provided air header placement, air flow rates, and baffling are adequate. Where these factors were inadequate,

extremely low overflow rates, such as those found at Flint River, seemed to compensate for the lack of an efficient design.

Effect of physical appurtenances on performance. The effective

operation of an aerated grit chamber depends on many factors, some of which are very difficult to evaluate. Good performance requires not only efficient operation, but also a unit which is relatively trouble-free, provides enough operational flexibility,

and yields good quality grit that can be easily handled and disposed. Results indicate that factors such as diffuser placement, type of grit removal equipment, air flow rate, and baffling were of greatest importance in achieving these goals.

The position of the air headers in relation to the direction of flow through the tank was crucial in establishing a proper flow pattern. Air header placement producing a spiral roll of

the water perpendicular to the flow through the length of the tank (R. M. Clayton and South River) seemed to minimize short circuiting. Center air feed (Utoy Creek and Flint River) and air headers placed to produce a wastewater roll parallel to

the direction of flow through the tank (Intrenchment Creek) promoted short-circuiting.

The use of inlet, outlet, and longitudinal baffles produced better tank hydraulics. At the Flint River grit chamber, a baffle at the submerged inlet port directed the incoming water toward the center of the tank, where a spiral roll could effectively be induced. At Utoy Creek, which had similar tank geometry and air header placement, the lack of such a baffle diminished ef fectiveness of the air source. The lack of an inlet baffle at the

R. M. Clayton grit chamber was offset by a high length-to-width ratio. At the South River grit chamber, a baffle at the inlet provided the hydraulic control necessary to prevent short-cir

cuiting across the length of the tank. A longitudinal baffle placed parallel to air headers at the R. M. Clayton grit chamber allowed better water circulation and reduced channeling. Thus hydraulic control can be improved by the installation of baffles where necessary.

Water content of removed grit is related to the type of grit removal equipment used. Screw and tubular conveyors (R. M.

Clayton and Intrenchment Creek) discharged a very dry grit. Grit washing (Utoy Creek and Flint River) did not seem to guarantee low organic content in the grit. In a long narrow tank

such as that at the R. M. Clayton plant, the extra length provided a washing effect that produced grit of very low organic content.

At the South River grit chamber the use of chain and buckets to remove and discharge the grit directly into a hopper without

washing caused excessive water carry-over and grit with high

volatility.

CONCLUSIONS

From the observations and data collected in this investigation, the following conclusions can be made:

A 95% removal of 65-mesh grit can be achieved in con

ventional aerated grit chambers and is a valid design criteria.

Table 3?Grit chamber performance data.

Parameter R.M. Clayton Utoy Creek Intrenchment Creek South River Flint River

Grit removal, wet basis, cm3/m3 treated wastewater 10.9 6.7 39.1 17.1 34.0

Grit quality TS, % 79 70 65 28 53 TVS, % 8 22 13 38 26

Percent removal of inerts equal or larger than 65-mesh 95.4 82.0 97.6 94.8 98.8

342 Journal WPCF, Volume 56, Number 4


Process Design

The removal of 65-mesh grit in full-scale grit chambers can be measured through sampling of the grit removed and primary sludge. However this methodology is not practical for routine performance evaluation.

Tracer studies are an excellent tool for performance eval

uation and troubleshooting of aerated grit chambers because

they easily identify areas where corrective action is needed to

improve performance. The shape of an aerated grit chamber is not necessarily the

key to good design. Proper diffuser header placement, a steady air source, and adequate baffling for hydraulic control are es

sential in establishing uniform flow pattern, which will improve performance.

Overflow rate does not seem to be a critical parameter in

the removal of 65-mesh grit, provided air header placement, air flow rates, and baffling are adequate.

Among the designs evaluated and for a typical detention time in the range of 3 to 5 minutes, a long, narrow tank provided the best unit process efficiency, grit quality, ease of operation, and adequate hydraulics. Such tank performance was less de

pendent on the use of influent and effluent baffles than that of square grit chambers.

Square grit chambers were effective in the removal of 65

mesh grit only if the air headers were positioned to create a spiral roll of the water perpendicular to the direction of flow through the tank, air flow rates were adequate to maintain uni

form velocities throughout the tank, and adequate hydraulic control was provided by the use of baffles.

Water content and volatility of the grit were related to the type of grit conveyor and washer used. Screw and tubular con

veyors discharged the dryest grit. Grit washing increased the water content significantly.

ACKNOWLEDGMENTS Credits. Operating personnel of the City of Atlanta water

pollution control plants provided assistance. W. H. Cross of

Georgia Institute of Technology and D. Sumlin and R. Bullard, directors at laboratories of the Bureau of Pollution Control and Bureau of Water of the City of Atlanta, respectively, provided some of the equipment and materials. Partial results of this

investigation were presented at the 1981 Georgia Water and Pollution Control Association Annual Conference.

Authors. At the time of investigation, Liliana Morales was

research engineer at the Division of Research and Development, Bureau of Pollution Control, City of Atlanta. Debra Reinhart is chief of the Division of Research and Development. Corre spondence should be addressed to Liliana Morales, CH2M HILL, 1941 Roland Clarke Place, Reston, VA 22091.

REFERENCES 1. "Wastewater Treatment Plant Design, MOP 8." Water Pollut. Con

trol Fed., and Am. Soc. Civil Eng., Lancaster Press, Inc., Lancaster, Pa. (1977).

2. Metcalf and Eddy, Inc., "Wastewater Engineering: Treatment, Dis

posal, Reuse." (2nd Ed.) McGraw-Hill, Inc. (1979). 3. Neighbors, J. B., and Cooper, T. W., "Design and Operation Criteria

for Aerated Grit Chambers." Water Sew. Works, 112, 12 (1965). 4. "Procedures for Evaluating Performance of Wastewater Treatment

Plants." Environ. Prot. Agency, Office of Water Programs, Wash

ington, D. C. (Contract 68-01-0107). 5. Finger, R. E., and Parrick, J., "Optimization of Grit Removal at a

Wastewater Treatment Plant." / Water Pollut. Control Fed., 52, 8 (1980).

6. Albrecht, A. E., "Aerated Grit Chamber Design and Operation." Water Sew. Works, 114, 9 (1967).

April 1984 343


Article Contentsp. 337p. 338p. 339p. 340p. 341p. 342p. 343

Issue Table of ContentsJournal (Water Pollution Control Federation), Vol. 56, No. 4 (Apr., 1984), pp. 151a-182a, 299-390, 183a-202aFront MatterDepartmentsAbstracts [pp. 170a, 172a, 174a, 176a]New Equipment, New Literature [pp. 171a, 175a, 177a]M-A Reports [p. 176a-176a]Washington Notebook [pp. 179a-181a]

EditorialBAT and Beyond [p. 299-299]

DepartmentsLetters [p. 300-300]

Errata: Application of an Ozone Disinfection Model for Municipal Wastewater Effluents [p. 300-300]Monitor30/30 Hindsight [pp. 301-305]

FeatureHistory of Water Pollution Control [pp. 306-313]

Plant OperationsChemical Selection and Operational Considerations for Filter Press Dewatering [pp. 314-318]On-Line Measurement of Respiration and Mass Transfer Rates in an Activated Sludge Aeration Tank [pp. 319-324]Making Full Use of Step Feed Capability [pp. 325-330]

Process DesignEvaluation of Filter Press Performance for Sludge Dewatering [pp. 331-336]Full-Scale Evaluation of Aerated Grit Chambers [pp. 337-343]Experimental Evaluation of the Significance of Overflow Rate and Detention Period [pp. 344-350]

Process ResearchSensory Analysis of Odorous Water Samples [pp. 351-354]Chemical Aspects of the Lime Seawater Process [pp. 355-363]Acclimation of Activated Sludge to Pentachlorophenol [pp. 364-369]Land Treatment of Contaminated Sludge with Wastewater Irrigation [pp. 370-377]

Industrial WastesNew Bleached Kraft Pulp Plant in Georgia: State of the Art Environmental Control [pp. 378-385]

CommunicationsDisinfection of Nitrified Effluents [pp. 386-387]Theoretical Estimation of Kinetic Parameters in the Design of Activated Sludge Processes [pp. 388-389]

DiscussionMethod for Estimating the Capacity of an Activated Sludge Plant [p. 390-390]

DepartmentsMarket Place [pp. 183a, 186a]People [p. 202a-202a]

Back Matter

Full-Scale Evaluation of Aerated Grit Chambers

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