DESTABILIZATION OF PARTICLES BY CHEMICAL 2 70 ~ 7 , p b ~ COAGULATION FOR TERTIARY FILTRATION

OF WASTEWATER EFFLUENT

Madhumanjari Ghosli City of Atlanta, Bureau of Pollution Control,

2440 Bolton Road N. W., Atlanta, Georgia 3031 8, USA

Appiah Amirtharajah School of Civil Engineering, Georgia Institute of Technology

Atlanta, Georgia 30332, USA

ABSTRACT

The purpose of this research was to determine process conditions for optimization of chemical pretreatment involving coagulation prior to the tertiary filtration of secondary (activated sludge) effluents. Bench scale studies involving coagulation with alum, settling and then filtration were conducted on secondary effluent samples. Two distinct mechanisms of coagulation were observed: (1) the mechanism of charge neutralization at alum dosages between 10 and 50 mg/l and pH values between 3.5 and 5 and the (2) the mechanism of sweep coagulation at alum dosages of 20 mg/l and greater and between pH 5.5 and 8.5. These regions when superimposed on the existing alum coagulation diagram for water, established new coagulation domains for filtration of chemically pretreated municipal wastewater effluent. Also an optimum design zone for particle destabilization was established where the effluent objectives were best met. This was found to be occurring at alum dosages of 55 to 60 mg/l and at pH values between 6 and 6.5. At the above conditions the BODS, TOC, turbidity, Total -P, and the orthophosphate levels of the secondary effluent were reduced by 73%, 57%, 98%, and 99% respectively after tertiary filtration. An altemative treatment scheme involving direct filtration of the secondary effluent was also studied and this was not found to be suitable for the particular effluent.

INTRODUCTION

Reclamation of wastewater is its treatment to make it usable and water reuse is the use of treated wastewater for a number of different purposes. The major benefit of wastewater reclamation and reuse is to enlarge the otherwise fixed quantity of water available for a given population. Whereas convenlional primary and secondary treatment practices succeed in removing or reducing the biochemical oxygen demand (BOD5) and total suspended solids (TSS) to a significant extent, treatment for reuse additionally requires that the above parameters be reduced to extremely low levels, with further reductions in nutrient content, color, taste, odor, and the complete removal of pathogenic organisms. This requires tertiary or advanced wastewater treatment to ensure microbiological or virological safety of the treated water. One of the principal tertiary treatment schemes include chemical destabilization followed by flocculation, sedimentation, filtration and disinfection. Alternatively, direct filtration without sedimentation is used. In this paper coagulation implies the overall process of destabilization and flocculation.

Secondary effluents contain a wide variety of suspended and colloidal particles that cause color and turbidity. Chemical destabilization and flocculation (coagulation) are the most important steps to remove colloidal particles and turbidity from wastewater and these processes are also quite effective in removing viruses. Historically there have been instances where optimization of the chemical destabilization-flocculation process and filtration of wastewater has been rather difficult to achieve. Since pretreatment plays such a dominant role in filtration, the

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I

coagulation diagrams for water developed by Amirtharajah and co-workers1~2J (Amirtharajah, 1988; Amirtharajah and Mills, 1982; Johnson and Amirtharajah, 1983) can be used as tools for predicting the conditions for particle destabilization and effective filtration.

Amirtharajah and Mills (15>82)2 presented the design and operation diagram for alum coagulation based on the hydrolysis equilibria of AI(II1). In this coagulation diagram the area defined as optimum sweep coagulation is the area for best settling floc, and is defined by the major parameters of alum dose of 20-60 mg/l and a pH of 7.0 to 8.0. The basis for this domain is not only the kinetics of coagulation reactions but also the rates of flocculation and sedimentation. In the corona region, the mechanism of destabilization is adsorption-charge neutralization. This area is suitable for direct filtration with low alum dosages and pH values of 6.8-7.5. For waters having colloids with low surface area, the coated colloid gets restabilized between pH 4.8 and 6.8 because of excess adsorption of positively charged species. Most often the zeta potential drops to zero on the boundary of the restabilization zone. These generalized concepts of coagulation of water (Amirtharajah and O’Melia, 19914) can be used to study the chemical dosages required for efficient filtration of wastewaters.

There are various parameters other than particle destabilization controlling effective granular media filtration of water. Kirkpatrick and Asano (1986)s evaluated the performance of two parallel tertiary treatment process trains. One was the chemically coagulated direct filtration process or the Filtered Effluent (FE) process and the other was a set of linked unit processes that included chemical coagulation with alum, clarification and filtration. The latter process train is referred to as the Title 22 (T22) process as it meets all treatment requirements of California Administrative Code, Title 22. The FE process involved a chemical dose of 5 mg/l of alum and 0.06 mg/l of anionic polymer and for the T22 process the alum dose ranged between 50 and 570 mg/l. It was observed that the T22 treatment train always achieved the effluent turbidity standard of 2 NTU whereas the FE process achieved about 85% compliance.

The Pomona virus study (hsano, Crites and Tchobanoglous, 1992)6 provided a comparison of the performances of the full treatment process (conventional scheme with alum dose 50-125 mgJl and polymer 0.2 mg/l) and an alternative and less costly tertiary process (contact filtration with 2-5 mg/l of alum and 0.06 mgll of anionic polymer). The following conclusions were drawn on the performance of the above processes, Firstly, water qualities, in terms of virus removal, from the two treatment processes were comparable when disinfection in the contact filtration scheme was performed with a high chlorine residual (10 mg/l). But the full treatment produced flocs in the sweep coagulation region, while contact filtration produced flocs under the sweep and charge neutralization mechanisms. Secondly, the stability of low-dose alum coagulation was affected by slight changes in wastewater pH (typically 7 to 7.5). Therefore during filtration with low alum doses pH control was essential. It was also concluded from all the above tests that to produce an essentially virus-free effluent using direct or contact filtration, the secondary effluent quality must be high. A secondary effluent turbidity value of 10 NTU is often considered the economic dividing line for using full treatment instead of alternative treatments like direct or contact filtration. However trickling-filter effluents typically have higher turbidity levels and direct filtration as a single treatment process cannot produce a final effluent to meet the turbidity standards (Faller and Ryder, lWl)7. Other parameters like chemical oxygen demand (COD) and TSS should also be considered during treatment. Many tertiary treatment plants recently designed in the United States use these alternative filtration processes.

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~ ~

MATERIALS AND METHODS

The wastewater samples for the research project, wire collected from the R.M. Clayton Wastewater Reclamation Center in Atlanta, Georgia. These samples were all activated sludge secondary clarifier effluents collected before chlorination. Table 1 presents the average levels of various characteristics of the secondary effluent from the above plant during 1992-1993 when the samples used for the research were collected.

A series of jar tests involving coagulation-sedimentation-filtration were performed with the wastewater samples at different alum dosages and pH conditions. The alum dosages ranged between 9 and 100 mg/l as Al2(S04)3.14.3H20 and the initial pH’s of the samples were adjusted by adding sodium carbonate (0.1 Normal) and these pH values ranged from 6 to 10 units. The samples were taken in 1-liter beakers and after alum injection, these were 1) rapid mixed at 100 rpm for 1 minute, slow mixed at 25 rpm for 20 minutes, and 3) settled for 30 minutes using a standard six paddle Phipps and Bird stirrer. After settling, the supernatants were passed through 2 column filters each containing 18-inches of anthracite coal (effective size = 1.0 mm, uniformity coefficient = 1.4). A ball valve, located at the bottom of the filter, was used to adjust the filtration rate. The flow used was 50 to 70 mL/minute. For the 2-inch diameter bench-scale filter columns, the above flow rates are equivalent to 0.59 to 0.83 gallons/minute/ft2 filter hydraulic loading rates. The settled and the filtered water samples were analyzed for residual turbidity and pH. The filtered water samples were also tested for BODS, total organic carbon (TOC), total Phosphorus (total-P), Ammonia-Nitrogen (NH3-N), and zeta potential. Direct filtration was also applied to the secondary effluent samples by filtering the coagulated water immediately after the slow-mixing step thus completely avoiding the sedimentation step. The alum dosages in these cases were lower and ranged between 2 and 50 mg/l. The resultant effluent was analyzed for turbidity and turbidity removals were estimated corresponding to various alum dosages.

The turbidity was measured using a Hach Turbidimeter. The zeta potential, used to determine the coagulation mechanism were measured with the help of a Zeta-Meter. The TOC concentration of the filtered effluents were measured using a Dohrmann DC-180 Carbon Analyzer. The total-P and the NH3-N concentrations in the samples were determined colorimetrically using a Technicon Auto Analyzer. The BOD5 was measured by following laboratory procedures outlined in Standard Methods (1985p.

RESULTS AND DISCUSSIONS

Turbidity Removal

Conventional TRatment

The first objective of the bench-scale testing was to define the best conditions for turbidity removal of the wastewater samples as a function of alum dosages and pH values. Jar tests at different pH and alum dosages were conducted to observe the variations in the effluent turbidities both after settling and filtration. It was observed that as the alum dose was varied (without keeping the pH constant) there were two distinct trends in the change in the settled turbidities, one in the low pH zone and one in the high pH zone. The data indicated that around pH values of 3.5 to 5, as the alum dose was increased, the settled turbidity removals initially increased, reached a maximum and decreased again. Around higher pH values of 5.5 to 9 the settled turbidity removals gradually increased and finally reached a constant maximum. These data are shown in Figures 1 and 2.

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These above phenomena can be explained if two different mechanisms for particle destabilization are considered, namely, charge-neutralization and sweep coagulation. At the lower arid narrower pH range the assumed mechanism of particle destabilization and coagulation is charge neutralization which occurs as a result of the interaction between the highly charged cationic aluminum hydrolysis species and the negatively charged colloidal particles present in the wastewater. A stoichiometric relationship exists between the positively charged and negatively charged particles and charge reversal of the colloids occurs by overdosing. This caused the settled water turbidity removals to go down after reaching a maximum value. On the other hand, for alum dosages greater than 20 mg/l and between pH 6 and 9, rapid formation of amorphous, solid phase aluminum hydroxide takes place and in this case turbidity removal occurs by the physical entrapment of the colloidal particle within the meshy hydroxide precipitate. As a result, instead of observing a maximum in turbidity removal an asymptotic approach to a steady value in the settled turbidity was noticed beyond a certain alum dosage.

However, the turbidity removals after filtration showed less drastic fluctuations at different pH and alum dosages although the data followed similar trend as that for settled water turbidities, defining the charge neutralization and the sweep coagulation zones respectively (see Figures 1 and 2). This was because, in almost all cases the flocculation step produced large and voluminous flocs, and any flocs not removed during sedimentation were removed by the column filters leaving the final effluent very clean and almost free of any suspended particles. As a result the variation in the settled water turbidities smoothed out considerably after the filtration step.

The occurrence of charge neutralization and then restabilization was further confirmed by the zeta potential data. The zeta potential of the secondary effluent was analyzed to be -30 mV. In the low pH zone of 3-5, it was observed that as the alum dosage was increased, the zeta potential of the resultant suspension after flocculation first increased in the positive direction due to the occurrence of charge neutralization and particle destabilization, and finally changed sign and acquired a positive value at higher dosages due to the occurrence of charge reversal and restabilization. The zeta potential data, coupled with the settled turbidity variations are shown in Figure 3. By interpolatirig the data, it was observed that a zeta potential of zero corresponded to an alum dose of about 63 mg/l which produced a corresponding settled turbidity of about 0.6 NTU and this value is close to the minimum turbidity level of 0.5 NTU. The actual minimum turbidity corresponded to an alum dosage of 68 mg/l and a zeta potential of about +5 mV.

.

The jar test data showed that more than 80% removal of turbidity of the wastewater were achieved in 55% of the samples after coagulation and settling and more than 96% removal of turbidity were achieved in 63% of the samples after coagulation- settling and filtration. The percent turbidity removals after settling and filtration as a function of alum dosage arid final pH are shown in Figures 4 and 5 respectively. The data indicated a sweep coagulation region bounded by pH 5.5 and 9 and dosages ranging from 20 to 90 mg/l closely resembling the same region for water coagulation. The best removal occurred between pH of 6 and 8 and alum dosages of 20 to 75 mg/l and this region was indicated as the region for optimum sweep. This result is consistent with Kirkpatrick and Asano (1986)5 who, in their study involving tertiary treatment of secondary effluent at Castroville Wastewater Treatment Plant, USA, observed this phenomenon of optimum sweep at an alum close of 50 mg/l and a pH value of about 7.0. In the charge-neutralization zone marked by pH 3 to 5 and alum dosages of 10 mg/l and more, the percent turbidity removals both after settling and filtration was slightly less than those at the sweep coagulation zone. The data in this region also indicated an upper boundary for

254

ma€ which was attributed to charge reversal and restabilization due to t u m i a n p m overdosing. The optimum sweep coagulation region is identified on the alum coagulation diagram in Figure 6. This region was found to be closely overlapping the same region for coagulation of water. Also this was the region where subsequently principal attention was focused to determine the variations in the concentrations of different parameters of the wastewater.

Direct RltmUl

. . ...

. .

Direct filtration tests were performed by eliminating the settling step. This scheme was found to achieve less turbidity removal than the ones with conventional full treatment. In these cases the final pH values after filtration were all kept within 6.4 to 7.4 and the alum dosages ranged from 2 to 50 mg/l to cover both the corona region and a substantial part of the sweep coagulation region in the alum coagulation diagram. All these tests resulted in higher values of filtered effluent turbidity than those obtained by conventional treatment of coagulation, sedimentation and filtration with the same process conditions, although the variation in the effluent turbidity in both cases followed the same trend. The results are given in Figure 7 and Figure 8. Although the effluent turbidity level of 2 NTU as required by the Title 22 Requirements of California was met in most cases, direct filtration was not recommended for tertiary treatment of wastewater from the R.M. Clayton plant if this quality standard is to be consistently achieved. This was because the secondary effluent turbidity from the plant frequently exceeded 10 NTU and the suspended solids level sometimes increased to above 20 mg/l. The above conditions are not ideal for conducting direct filtration of the secondary effluent (Wastewater Engineering, 1991)g. The above results may be significantly improved by the simultaneous use of alum and some anionic polymer.

BOD5 and TOC Removal

It was decided to look at the change in the BOD5 and the TOC values in the ‘optimum sweep’ region after the wastewater was subjected to conventional full treatment of coagulation with alum, sedimentation and filtration through the column filters. Jar tests simulating conventional treatment with alum dosages ranging from 20 to 70 mg/l were conducted and sodium bicarbonate (0.1 N) was added initially to the secondary effluent such that the pH values of the final treated effluent were within 5.5 and 9.5. The initial BOD5 of the secondary effluent was quite low and varied between 9 to 12 mg/l and it was observed that the final treated BODS ranged from 1.1 to 5.5 mg/l depending on the dosage and the pH. However the final levels were independent of the initial BODS level. The results when plotted (see Figure 9) indicated that for all dosages, the best removals occurred around pH 6 to 6.7 and then decreased with increase in the pH level.

The above procedure was also carried out to find the changes in the level of TOC after physico-chemical treatment with alum. The TOC removals were found to be proportional to the removals in the BODS although they were numerically less. The initial TOC level of the secondary effluent was around 11 mg/l and those after the treatment varied from 4 to 6.7 mg/l. The results are presented in Figure 10 and show a trend similar to the one observed for BODS. The best removal occurred around pH 6 to 6.7 and decreased as the pH was raised. The BOD5 removals were consistently higher than that for TOC for a particular alum dosage and pH and so it was concluded that by destabilization-focculatioil-s~dimentation-filtration of an activated sludge effluent more biodegradable carbon was removed compared to total carbon including refractory organics.

255

Total-P and NH3-N Removal

Eutrophication is one of the major problems in the streams and rivers in the -y the effectiveness of removal of nutrients N and P, by tertiary treatment was also evaluated. Conventional treatment including coagulation with alum, sedimentation and finally filtration was applied to the secondary effluent to determine the effluent ammonia and total phosphorus (total-P) levels in the ‘optimum sweep’ region. It was observed that below a dosage of 55 mg/l there was incomplete removal of the total-P, but a higher dosage achieved more than 99% removal in the total-P. The best pH range for these removals were found to be between pH 6 and 6.8. The results are shown in Figure 11. Above a pH value of 7.3 there was hardly any reduction in the total-P level irrespective of the alum dosage. The initial total phosphorus level of the secondary effluent was 1.5 mg/l and after 99% removal the final phosphorus level was significantly lower than 0.75 mg/l which was the stream discharge criterion. However, the orthophosphate fraction of the total phosphorus was more readily removed even at lower alum dosages (see Figure 11). The orthophosphate removals corresponded to about 80% at an alum dosage of about 10 mg/l and increased with increase in the dosage and reached more than 99% for an alum dosage of 36 mg/l and higher. This was because the orthophosphates were removed by the ready precipitation of aluminum phosphate. The rest of the phosphorus, comprising polyphosphates and organic phosphorus were removed less readily, probably by a combination of more complex reactions and sorption on floc particles (EPA, 1976)lO.

There was no reduction in the levels of ammonia-nitrogen (NH3-N) after coagulation and filtration of the secondary effluent with alum. However, the stream discharge limit for NH3-N during January 1993 when this particular study was being conducted, was 20 mg/l which was considerably higher than the level in the secondary effluent which was around 2.4 mg/l. Also the pKa for ammonia is 9.2 and below a pH of 8.5 ammonia mostly exists as ammonium ion which is not toxic to fish. Since the pH of the secondary effluent was around 6.7 units, the chances of fish toxicity were limited.

Determination of Optimum Design Conditions

The optimum design conditions of chemical pretreatment for tertiary filtration of secondary effluent from the R. M. Clayton Wastewater Reclamation Center was determined based on the removal data for various parameters like turbidity, BODS, TOC, total-P, and NH3-N. From the BOD5 and TOC removal data, it was noted that the best removal occurred between pH 6 and 6.7 and in that pH range, an increase in the dosage from 36 to 70 mg/l did not affect the removal significantly. From the total-P removal data, it was observed that the lowest alum dose required to achieve more than 99% removal was 55 mg/l and in the pH range of 6 to 6.5. Also the turbidity removal data had shown that at a pH of 6 to 6.5 , an alum dose of about 55 mgfi could reduce the effluent turbidity by about 8 1 % after coagulation and settling and by 98% after coagulation, settling and filtration. Therefore it was concluded that coagulation with an alum dose of 55 to 60 mg/l in the pH region of 6 and 6.5 was the best pretreatment condition for particle destabilization for filtration of the secondary effluent of the R.M. Clayton Wastewater Reclamation Center. This region is shown on the alum coagulation diagram in Figure 12. Operating the treatment process under these conditions will produce the results shown in Table 2.

SUMMARY AND CONCLUSIONS

Bench-scale tests were performed with secondary effluent from the R.M. Clayton Wastewater Reclamation Center in Atlanta, Georgia, to optimize the chemical pretreatment processes for tertiary filtration of the wastewater effluent. Since the

256

raticrrratoperatrorrpach was to choose the lowest chemical dose that achieves the best effluent objective, the optimum conditions for particle destabilization were determined to be: an alum dosage of 55 to 60 mg/l at pH values of 6 to 6.5. This optimum condition was evaluated for the conventional treatment consisting of destabilization, flocculation, settling and filtration. The following paragraph summarize the turbidity, BODS, TOC, total-P, and orthophosphate removals observed at the optimum design condition.

At the optimum design condition, the turbidity of the coagulated-flocculated-settled wastewater effluent was reduced by more than 80% lo reach a final value of about 1.5 NTU. The turbidity of the coagulated-settled-filt.ered effluent was lowered by 98 % and reached a final effluent level of about 0.12 NTU. For the coagulated- settled-filtered wastewater effluent, it was observed that at the optimum design condition, the BOD5 of the sample was reduced by a maximum of 73% with a final effluent level ranging between 1 and 2.5 mg/l and the TOC was reduced by 57% with a final effluent level of approximately 4.2 to 4.5 mg/l. At this condition, both the orthophosphate level and the total-P level of the effluent were reduced by more than 99% from initial values of 0.4 and 1.5 mg/l respectively.

Two distinct mechanisms of coagulation were observed with the secondary effluent: (1) the mechanism of charge neutralization at alum dosages between 10 and 50 mgll and pH values between 3.5 and 5, and (2) the mechanism of sweep coagulation at alum dosages of 25 mg/l and greater between pH values 5.5 and 8.5.

Greater particle destabilization and turbidity removal were observed when the wastewater samples were subjected to conventional treatment consisting of destabilization, flocculation, settling and filtration compared to the case when the secondary effluent was subjected to the direct filtration process (without settling) consisting of destabilization, flocculation and then filtration for the same pH and alum dosage.

An important aspect of the research was that it illustrated a methodology for using bench scale tests with the coagulation diagram to optimize chemical coagulation for tertiary treatment of wastewater effluent in terms of overall quality measured by several parameters such as turbidity, BODS, TOC, and total-P.

ACKNOWLEDGMENT

This research was conducted when Madhumanjari Ghosh was a graduate student in the Environmental Engineering Program at the School of Civil Engineering, Georgia Institute of Technology (USA) and was partially funded by the United States-Israel Binational Science Foundation. Any questions or comments regarding this paper should be directed to Madhumanjari Ghosh.

REFERENCES

1. Amirtharajah, A. (1988). Some Theorelical and Conceptual Views of Filtration. Journal of the American Water Works Association, 80,36-46.

2. Amirtharajah, A., and Mills, K.M. (1982). Rapid..Mix Design for Mechanisms of Alum Coagulation. Journal of the American Water Works Association, 74 (4), 210-216.

3. Johnson, P.N., and Amirtharajah, A. (1983). Ferric Chloride and Alum as Single and Dual Coagulants. Journal of the American Water Works Association, 75, 232-239.

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4. Amirtharajah, A., and O’Melia, C.R. (1991). Coagulation Processes: Destabilization, Mixing and Flocculation, Chapter 6 in Water Quality and Treatment, American Water Works Association (Ed), 4th ed., McGraw-Hill Inc., New YorkJJSA, 269-355.

5. Kirkpatrick, W., and Asano, T. (1986). Evaluation of Tertiary Treatment Systems for Wastewater Reclamation and Reuse. Water Science and Technology,

6. Asano, T., Richard, D., Crites, R., and Tchobanoglaus, G. (1992). Evaluation of Tertiary Treatment Requirements in California. Water Environment and Technology, 4 (2): 36-40.

7. Faller, J.A., and Ryder, R.A. (1991). Clarification and Filtration to meet Low Turbidity Reclaimed Water Standards. Water Environment and Technology, 3 (1):

18 (lo), 83-95.

68-74.

8. Standard Methods for the Examination of Water and Wastewater, (1985). 16th edition, published by American Public Health Association, American Water Works Association, and Water Pollution Control Federation, Washington D.C.

9. Wastewater Engineering: Treatment Disposal and Reuse (1992) by Metcalf and Eddy, Inc., revised by Tchobanoglaus, G., and Burton, F. 3rd edition, McGraw Hill, New York, N.Y., 1992.

10. Process Design Manual for Phosphorus Removal (1976). EPA-600/1-76-001a, Environmental Protection Agency.

11. Ghosh, M. (1993). Chemical Pretreatment for Particle Destabilization in Wastewater Efluent Filtration. Unpublished Master’s Special Research Problem Report, School of Civil Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA.

12. Asano, T., Tchobanoglaus, G., and Cooper, R. (1984). Significance of Coagulation-Flocculation and Filtration Operations in Wastewater Reclamation and Reuse. Water Reuse Symposium Proceedings, 3: 1 184- 12 15.

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100

80

60

40

20 2’5 5 0 75 1

Alum Dose (mgh)

Figure 1. Percent Turbidity Removal of Secondary Effluent after Settling and Filtration in the Charge Neutralization (low pH) Region (Initial pH = 6.2, Turbidity = 6.2 NTU)

80 -

60 - 4oj J j-1 + Setlled Sample

20 i I I I

0 25 50 1 5 I

Alum Dose (mgll)

I

I

Figure 2. Percent Turbidity Removal of Secondary Effluent after Settling and Filtration in the Sweep Coagulation (high pH) Region (Initial pH = 9.8, Turbidity = 5.6 NTU)

259

10

5

0

- 5

-10

-15

-20

-25

-30

0 2 0 40 60 8 0 100 Alum Dosage (mgh)

3

2.5

2

1.5

1

0.5

0

Figure 3. Variation in Turbidity and Zeta Potential of the Settled Effluent as a function of Alum Dose (Initial pH = 6.93, Initial Turbidity = 11.5 NTU) I

Restabilization Ophmum Sweep

................... i .......................................................................... ......................................

.................. .i ................... i. ................. .:. ................ ..I.. . SWWR .Cp1om(IIli.90.. ............ {. ................. ........................................................................... ' ......................................

....... More than 80% Removal _ _ _ _ _ _ hsa than 804b Removal

: I I I I I 4 5 ti 7 8 9

pll d Mixed Solution

Figure 4. Percent Turbidity Removal of Secondary Effluent after Settling as a Function of Alum Dose and pH (Initial Turbidity = 4 to 8 NTU)

260

100-

10-

17 3

...................................

............................ 9, ........................

................................

. . . . . . . . . . . . . . .

I 4 6 7 8 9 pH of Mixed Solution

Figure 5. Percent Turbidity Removal of Secondary Effluent after Settling and Filtration as a Function of Alum Dose and pH (Initial Turbidity = 4 to 8 NTU)

-7 i pH of Mined Solution

300

30 3 E

X 6,

3 4 m s

E U 3 e U

0.3

0.03

Figure 6. Alum Coagulation Diagram Showing Various Coagulation Regions for Water and Wastewater

261

I I I I I

Alum Dose (mgA)

Figure 7. Comparison of Turbidity Removal by Direct Filtration and Conventional Treatment as a Function of Alum Dose (Initial Turbidity = 13 NTU, Final pH = 6.4 - 6.6)

100,

95 ' 3 !3 0

d $ 90'

E

.r( n 5 b

e: 8 5 , 8 u

80,

'-s- Conventional Treatment

I I Direct Filtration

0 5 10 15 20 25 c

.Alum Dose (mgfi)

Figure 8. Comparison of Turbidity Removal by Direct Filtration and Conventional Treatment as a function of Alum Dose (Initial Turbidity = 12 NTU, Final pH = 7 - 7.3)

262

loo'

100

80 - 7 i2

60-

E+

8 40- Y E:

n"

2

a" 8

0

d

c

n"

.-$- Alum Dose = 75mg/l

.+- Alum Dose = 60 mgA

__o__ Alum Dose = 40 mgfl

-++- Alum Dose = 25mgA

40 __c_ Alum = 60 mgA

.-t- Alum = 40 mgh

$+~ Alum = 25 mgA 20 I I I

5 6 7 8 9 pH of Mixed Solution

Figure 9. Percent BOD5 Removal from Secondary Effluent after Coagulation, Settling, and Filtration in the Optimum Sweep Coagulation Region (Initial BOD5 = 9 - 12 mg/l)

I 5 6 7 8 9

2 0 1 '

pH of Mixed Solution

Figure 10. Percent NPOC Removal of Secondary Effluent after Coagulation, Settling, and Filtration in the Optimum Sweep Coagulation Region (Initial NPOC = 1 1 mg/l)

263

100 - 75 - 3

8 50-

0 E c) e: Q)

a 8 25-

O ! I I I

Total-Phosphorus

-3

4 -

-5 -

4j -

Restabiliz lor Waster

Charge Neutrrliut

..........................................

..............................................

....................................

-7 L 0 4 6 8

pH of Mixed Solution

300

30

3

3 B 0

54 X m i

v1

4 r, 0 - I

0 3

0.03

Figure 12. Alum Coagulation Diagram Showing the Optimum Design Condition for Particle Destabilization for Tertiary Filtration of Secondary Effluent

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Table 1. Average Levels of Various Parameters for Secondary Effluent from the R. M. Clayton Wastewater Treatment Plant During 1992-1993.

Average Value

I TSS c ih i i i Turbid& @TU) Total-P (mg/l) NH3-N (mgll) Alkalinity (mgll) as CaCG Temperature ( deg C) DH

19 1 1

2.4 2.4

65 to 85 18 to 22

6.7 260

r - -

Sp conductance (VSiemenslcm)

Table 2. Summary of Various Wastewater Parameters After Applying Tertiary Treatment at the Optimum Design Condition

Turbidity BOD5 NPCIC Total-P NH3-N

Wastewater (NTU) (mg/l) (mg/l) (mg/l) (mdl) - Secondary 6 - 14 7 -13 10 - 1 1 1.3 -2.6 2.2 -2.6 Effluent from the R.M. Clayton Plant

Tertiary Effluent 0.12 1 - 2.5 4.2 - 4.5 < 0.1 2.2 - 2.6 after optimum Chemical Treatment

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