Virus removal by adsorption in treatment processes

74

Waste Water Treatment

Flnldization of floes produced in chemical or biological treatment plants. F. EDELINE*, I. TESAI~IKt, J. VOSTR~IL$, *Centre Belge d'Etude et de Documentation des Eaux, Li6ge, Belgium. tTechnical College, ~ilina, Czechoslovakia. :~Hydraulic Research Institute, Brno, Czechoslovakia Fluidization of flocs produced by chemical coagulation is used for removal of colloidal and suspended matters in sludge blanket clarifiers. Fluidization of biological flocs takes place in activated sludge secondary tanks of the upflow type. The fluidization of rigid particles may be expressed by the simple exponential equation of Richardson and Zaki. In the present work, an attempt has been made to generalize this equation of fluidization to flocs produced in chemical treatment of water and in biological purification of waste water and sewage. The equation is as follows: v = Vo. 8= in which v -- superficial velocity; vo = free settling velocity of a single particle; 8 = void fraction; = = exponent, which should be about 2.5 for turbulent flow, and > 5 for laminar flow. Unfortunately it is rather difficult to determine with accuracy the value of the void fraction and suspension density. Crucial experiments have been performed in order to find the exact value of porosities and densities by the following methods: (1) settling of a sample in a definite time interval; (2) centrifugation of a sample; (3) introduction of a tracer in the fluidized bed; (4) pycnometric method; (5) drying. These methods have been compared and evaluated statistically. The experiments have shown that the exponential law may be taken for granted even for flocculated matter. However the mechanism of floe formation in the fluidized bed shows some differences in the two cases, as explained by the following phenomena. The chemical flocs will be destroyed by turbulent fluctuations if no chemicals are added to the raw water. On the contrary, the biological flocs withstand the inertia forces of the stream without being disrupted. The results are based on experiments performed with low and high turbidity raw water. The chemicals used for the coagulation were: aluminium sulphate, ferric chloride, chlorinated ferrous sulphate. In some cases, coagulation aids have been applied, such as activated silica, synthetic polyelectrolytes of the anionic and cationic types. In the case of biological treatment, we have worked with flocs from household sewage and dairy wastes. In the paper is discussed the respective value of the exponent a and the free settling velocity Voin the cases mentioned. Drawings are given for the most important experimental and industrial apparatus.

Virus removal by adsorption in treatment processes. OTIS J. SPROUL, O r o n o , Maine, U.S.A. Virus inactivation may be affected by a number of mechanisms. Among these mechanisms are: (I) loss of the protective protein coat by enzymatic action. (2) denaturation of the surface protein coat. (3) loss of structural integrity by pH effects. (4) alteration of the nucleic acid core or surface protein by oxidants and organic or inorganic toxicants. (5) adsorption to various surfaces. All of these mechanisms may operate in waste water treatment plants but the most important of these is the adsorption process. Cmu.soN et aL (1966) have previously shown the importance of adsorption in the removal of viruses in natural waters.

Waste Water Treatment

75

It is the objective of this paper to present original information on the removal of viruses by adsorption processes. The processes will include tertiary and secondary waste water treatment processes. EXPERIMENTAL

PROCEDURES

AND

MATERIALS

The viruses used in our laboratories have included the T2 bacteriophage and the Type 1 poliovirus (Sabin). The culture techniques for the bacteriophage and poliovirus have been reported earlier NIxoN (1965), HAKANI) and GELFANO (1962). The T2 bacteriophage was generally used in tiers of about 1 × l0 s P F U (plaque forming units) per ml and the poliovirus in titers of about 30,000 to 50,000 PFU/ml. The suspending medium has been either a biologically treated (trickling filter or activated sludge) effluent or a distilled water to which various salts have been added. Additional details on the water characteristics will be presented in the paper. The experimental procedures have used bench scale equipment. A portion of the work on activated carbon adsorption used a bench scale continuous flow glass column apparatus. The remainder of the work has been carried out in small glass reaction vessels. Further experimental details will be presented in the paper. RESULTS

AND

DISCUSSION

Tertiary treatment processes Activated carbon adsorption. Adsorption of the T2 bacteriophage from the secondary effluent to activated carbon was preceded by a study to determine the equilibrium conditions for the adsorption. The adsorption isotherms ((Freundlich) showed a curved plot for the virus with a decreased equilibrium of virus/g of carbon under higher conditions of virus and COD remaining. This was indicative of a competitive adsorption condition in which the organic matter (measured as COD) displaced the virus from its adsorption sites on the carbon. This competition was expected since the adsorption of the virus by carbon is thought to be a surface phenomenon. The removals obtained at equilibrium for the virus and organic matter with a concentration of 0.25 g of activated carbon per 100 ml of suspending liquid is shown in TABLE 1 for four powdered activated carbons. Thes West Virginia Nuchar (2-190 gave the greatest removal of viruses at equilibrium and very nearly the highest removal of COD. This carbon was used for the further studies. The continuous flow studies were performed with a glass column which required 9.4 g of the carbon to give a 6 in. deep bed. The mesh size of the Nuchar C-190 carbon used was 4 × 30. The extent of removal of the virus was determined by titering the virus which remained in the stock bottle used to charge the column and comparing this with the titer in the effluent from the carbon column. This investigation indicated that the exhaustion point for the viruses was reached long before the exhaustion point for the organic matter. The flow-through volume before the exhaustion point was TABLE I . EQUILIBRIUM VALUES FOR VIRUS AND ORGANIC MATTER ADSORPTION ON VARIOUS ACTIVATED CARBONS

Type carbon

Pittsburgh West Virginia Nuchar C-190 American Norit Columbia Arc

Initial virus (104PFU/ml)

Virus removed (~o)

Initial COD (mg/1)

COD removed (~/o)

72 89 73 58

32 75 29 45

71 69 67 62

28 46 41 47

Conditions: 0.25 g carbon per 100 ml of secondary effluent. reached was dependent upon the flow rate of the liquid. This varied from about 8.5 1. at a flow rate of 0.5 gal/min per ft. 2 to about 21 1. at a flow rate of 8 gal/min per ft. z The maximum adsorption of the virus and the organic matter occurred early in the filter run and was dependent upon the flow rate. This is illustrated in Fzo. 1. A rather sharp break at a flow rate of 3 gal/min per ft" was noted

76

Waste Water Treatment

for the adsorption of the viruses. Increases in the flow rate from this point still gave a maximum removal of about 10 per cent. An analysis of the continuous flow runs indicated that when the r u n continued beyond the exhaustion point for the viruses the titers in the virus coming through the column were greater than those in the influent. This indicated a desorption of the viruses from their adsorption sites. This had been predicted from the equilibrium studies. 70_

o

60

Virus

o COD

50 0 u c

7 8 4°-

.~. E

°'30

20

E o

I0 -'~

o 0

o

o~

I

I

r

I

t

T

I

I

I

2

3

4

5

6

7

8

Flowrate,

gal/min per ft z

FIG. 1. Maximum virus and COD adsorption at different liquid flowrates. Additional work is now being done on the adsorption conditions of the Type 1 poliovirus to the Nuchar C-190 and will be reported on in the paper. It is expected that the extent of desorption will be less than with the T2 virus since the poliovirus has a much smaller dimension (10 mp vs. 1000 rap). Phosphate adsorption. The removal of the poliovirus by adsorption to precipitating calcium phosTABLE 2. T Y P E 1 POLIOVIRUS REMOVAL FROM A SECONDARY EFFLUENT BY PHOSPHATE PRECIPITATION W I T H CALCIUM HYDROXIDE

Initial test conditions Parameter Test number PO4- a (mg/1) Ca(OH)~(mg/l)

1 42 --

2 42 45

3 42 45

4 42 91

5 42 91

6 85

7 85 91

8 85 91

9 85 182

--8.1 37 --

15 63 10.3 2.2 94

17 3.7 68 116 10.3 11.2 4.9 0.83 87 98

10 85 182

Final test conditions PO4- 3(rng/l) Hardness mg/l as CaCO3 pH Poliovirus (PFU/ml × 10 a) Poliovirus removal (Yo)

-24 22 11 12 -130 132 152 157 6'9 9.1 9.3 10-2 10.3 33 12 8.9 6.4 5-5 -63 73 81 83

43 125 11-3 0-39 99

Initial conditions--pH 6.8, hardness 131 mg/l, alkalinity 68 mg/l. Test number 1 is the control for 2-5; 6 is the control for 7-10. phate is presented in TARLE 2. The orthophosphate content of the secondary ettluent used was 42 rag/1 as phosphate. This natural phosphate concentration was reacted with the stoichiometric amount of calcium hydroxide, 45 rag/l, and twice the stoichiometric amount, 91 mg/l. The remaining phosphate

Waste Water Treatment

77

under these conditions was about 23 and 12 rag/1 respectively. The per cent poliovirus removed averaged 68 and 82 per cent respectively. Increasing the phosphate to an initial value of 85 rag/1 by the addition of sodium phosphate and its removal by a stoichiometric and twice the stoichiometric amount of calcium hydroxide gave increased removals of the poliovirus. These removals averaged 90 and 98 per cent respectively. It may be noted that when 182 mg/1 of calcium hydroxide was added the pH under these conditions reached 11.2 and 11.3. This is just below the critical pH range for inactivation of this strain of poliovirus from pH considerations. The removals obtained here should, therefore, be attributed to the removal within the precipitation process. These data indicates that the poliovirus removal was dependent upon the amount of calcium phosphate precipitate produced and, therefore, indicates an adsorption reaction. The high removals obtained in this process are about those which have been reported for the activated sludge treatment of waste water. It is thought that the removal of the poliovirus under these conditions is caused by hydrogen bonding with the phosphate groups which are being precipitated and/or by the formation of a phosphoprotein. The types of proteins on the surface coat of the poliovirus are such that the formation of phosphoproteins is likely (LEvrrcrow and DARNELL, 1960; FRUTONand SIMMO~a3S,1958). The formation of an insoluble calcium product with the proteins in the surface coat of the poliovirus is also possible. The precipitation of this product would result during the formation of a calcium carbonate precipitate. TABLE 3 shows that removal of the potiovirus was obtained when a calcium

TABLE 3, TYPE 1 POLIOVIRUS REMOVAL BY CALCIUM CARBONATE PRECIPITATION WITH LIME

Calcium bicarbonate rag/1 as CaCO3 Initial

Final pH

Residual

100 200 300 400

36 59 82 100

9-0 8.2 8-0 8"0

Virus inactivation (~o) Run 1

Run 2

26 35 63 71

0 51 77 90

carbonate precipitate was formed. Similar data for the T2 virus was obtained by TrXAY~Rand SPROUL (1966). If removals at equal concentrations of calcium in the precipitated form are compared, the removals of virus are significantly less in the calcium carbonate system. In tests 9 and 10 in TABL~2, 98 and 99 per cent removals were obtained when 51 mg/1 of calcium was precipitated in the form of calcium phosphate (or 68 rag/1 ff the precipitated product is calcium apatite). The precipitation of as much as 72 mg/l of calcium as a calcium carbonate precipitate (100 mg/l initial calcium carbonate, TABLE3) resulted in removals of only 0 and 26 per cent in runs 1 and 2. On this basis it would appear that the formation of phosphoproteins was more important in the removal of poliovirus by precipitation of calcium phosphate. Secondary treatment process

The mechanisms of inactivation of viruses in the activated sludge process have not been determined. It has been shown by CLARKEet aL (1961) that the removal can be described by a Freundlich adsorption isotherm. Work is presently underway to determine the role of adsorbed phosphate on the bacterial sludge in the inactivation of viruses. It is known, from the above discussion, that the formation of phosphoproteins is an important adsorption mechanism in the removal of virus by this process. This is further supported by SA~a)ERSONand KELLY (1964) who reported that increased inactivation of virus occurred when phosphate was added to an activated sludge system. These data presently being obtained are to determine the effects of variation in phosphate concentration with sludge mass, age of the sludge and pH and temperature of the system. FW

78

Waste Water Treatment SUMMARY

AND

CONCLUSIONS

The following statements and conclusions can be made on the data presented here. I. Activated carbon adsorption of the T2 virus from a secondary effluent indicated a competitive adsorption with the organic matter for the available sites. 2. The adsorption of the T2 virus on activated carbon in continuous flow operation showed a marked dependence upon the flow rate. The exhaustion point for the virus was reached before the same point for the organic matter. Desorption of the virus was noted as the run continued beyond the virus exhaustion point. 3. Removals of up to 99 per cent of a poliovirus were obtained by the precipitation of 81 mg/1 of phosphate with calcium. 4. The formation of phosphoproteins is more important than the formation of insoluble calcium protein products in the inactivation of Type I poliovirus by adsorption on calcium phosphate. 5. The adsorption of viruses on activated sludge is phosphate dependent. The parameters controlling this mechanism will be reported on in the full paper. Acknowledgement--This work was supported by a Federal Water Pollution Control Administration research grant WP-00387-03. REFERENCES CARLSON G. F., JR., WOODWARD F. E., WENTV~ORTHD. F. and SPROUL O. J. (1966) Virus inactivation in natural waters--1. Virus inactivation on clay particles. Presented at the Annual Meeting Water Pollution Control Federation Kansas City, Mo., September 1966. CLARKE N. A., STEVENSONR. E., CHANG S. I. and KASLER P. W. (1961) Removal of enteric viruses from sewage by activated sludge treatment. Am. J. pub. Hlth. 51, 1118. FRUTONJ. S. and SIMMONDSS. (1958) General Biochemistry. John Wiley, New York. LEVINTOWL. and DARNELLJ. E., JR. (1960) A simplified procedure for purification of large amounts of poliovirus: Characterization and amino acid analysis of Type 1 poliovirus. J. bioL chem. 253, 70. NAKANOJ. S . and GELFANDH. i . (1962) The use of a modified Wecker Technique for the serodifferentiation of Type 1 polioviruses related and unrelated to Sabin's vaccine strain--I. Standardization and evaluation of the test. Am. J. Hyg. 75, 363. NIXON F. P. (1965) The effects of ions on removal of viruses from water by polyelectrolytes. M. Sc. thesis, University of Maine, Orono. Me. SANDERSONW. W. and KELLY S. (1964) Discussion of Paper entitled: Human enteric viruses in water: Source, survival and removability. Advances in Water Pollution Research. 11, 536, MacMillan Company, New York. THAYER S. E. and SPROULO. J. (1966) Virus inactivation in water softening precipitation processes. d. Am. War. Wks Ass. 58, 1063.

Investigations on the control of sphaerotilus sludge. A. PASVEER, D e l f t , H o l l a n d THE AIMS

OF THIS INVESTIGATION

1. To gain knowledge of the conditions which encourage development of a Sphaerotilus sludge in an oxidation ditch system. 2. To find out why once a Sphaerotilus sludge has developed, it proves to be very difficult to recover the normal properties of the sludge. 3. To find conditions in which the growth of Sphaerotilus is suppressed. 4. To operate the oxidation ditch system (activated sludge system) so that the opportunity of Sphaerotilus to grow is reduced to a minimum. THE

METHOD

OF APPROACH

I. Regular investigation of the sludge properties and of the composition of the purified effluent in two oxidation ditches in which a Sphaerotilus sludge had developed