Virus removal by the domestic waste water treatment system named johkasou

~

Pergamon

Waf. Sci. Tuh. Vol. 3S. No 11-12. pp. 187-191. 1997.

C 1997 IA wQ. Published by Elsevier S<:ience Ltd

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VIRUS REMOVAL BY THE DOMESTIC WASTEWATER TREATMENT SYSTEM NAMED JOHKASOU M. Kaneko Department ofIndustrial and Systems Engineering. Setsunan University. 17-8. Ikedanako.machi. Neyagawa, Osako.. 572 Japan

ABSTRACT Virus removal by a treatment plant for domestic wastewater (Johkasou). was invesligaled using a small model oflhe planl. Under standard BOD loading of 0.076 BOD kglm 3/day. 97% of E. coli phage 12, 98% of poliovirus I and 93% of coxsacluevirus B3 were removed from mlet wastewater by the system. About 80% of the viruses in the influenl were removed 10 the first and second anaerobic zones under lhe standard conditions. When the loading was increased 10 double the standard 1000ing (0.152 kg BOD/m 3/day) the removal rate decreased 10 64%. Pohovirus I and coxsackievirus B3 were removed more easily than 1'2 phage. Assuming lhe Slream in each zone was complelely mixed, the Virus reducIng activily of microorganisms was estimaled by Ihe rate constant of lhe first order reduction equation. It was found thaI the higher the BOD loading rates, lhe lower the values of the constanl.
KEYWORDS Johkasou; E. coli T2 phage; poliovirus; coxsackievirus; aeration tank. INTRODUCTION To be microbiologically safe in public waters, even small wastewater treatment systems should have the capacity to reduce hazardous microorganisms. Although there are many studies on virus removal in sewage treatment systems, few investigations have examined virus removal in small treatment systems used domestically. The small treatment systems for domestic wastewater named Johkasou are popular in Japan. which are set up around areas where sewerage systems are not laid (JECES, 1994). This study investigated the virus removal capacity of Johkasou using two kinds of enteroviruses (polio and coxsackie) and a bacteriophage (12 phage). MATERIALS AND METHODS

Viruses and host cell - poliovirus I LSc2ab and coxsackievirus B3 were grown and plaque assayed in BOM cells. T2 phage, selected as an indicator virus, was propagated in Escherichia coli B and enumerated by plaque assay.

187

188

M.KANEKO

Johkasou - the model of one of the Japanese Johkasou systems was used at 20°C. The system is named "anaerobic filter contact aeration process" consisting of four compartments: primary anaerobic zone. secondary anaerobic zone, aeration zone with contact media and final settling zone. It is one-eighth the size of the actual plant which is applied to the treatment of wastewater discharged from ten persons.. Operating conditions - BODS concentration in the influent into which viruses were added was 172mgIL. The BOD loadings applied to the model and the retention times in each part of the model were controlled by changing the flow rate of the influent with dilution water as shown in Tabl~ I. The BOD loadings were determined on the assumption that one person discharges 43g of BOD and 250L of water per day with the result that the standard loading for the Johkasou system is O.076kglm3/day. The organic contents in treated waters were measured by COD. The BOD loading in Condition-2 shown in Table 1 corresponds to that usually applied to actual plant. The BOD loadings in Condition-I, Condition-3 and Condition-4 were 0.7. 1.5 and 2 times as much as the standard condition (Condition-2) respectively.

Table 1. Retention time and BOD loadings applied to the model 2 Condition Anaerobic tank 50.9 34.0 Retention time (h) Aerobic tank 31.1 20.7 12 I 8.1 Sedimentation tank 0,48 072 BOD loading to the system (glday) 0.076 BOD loading per volume (kg 0.051 BOD/ml/day) t standard condition applied to actual plant ofJOHKASOU

3 22.6

4

5.4

17.0 10.4 4.1

1.08 0.114

0.152

13.8

1.44

t 336 19.2 6.7 430 0.078

RESULTS COD removal rates in Condition-l and Condition-3 were comparable to that in the standard condition. When the BOD loading was twice the standard condition, the treatment activity deteriorated giving high COD values in the effluent. About 50% of influent COD was removed in the first anaerobic zone that was located at the first stage in the system. Although COD reduction at the first anaerobic zone was not influenced by the BOD loadings. the reduction at the second anaerobic zone was markedly affected by the loadings. While the second anaerobic zone was found to yield 83% COD removal under Condition-I, the same zone achieved only 12% COD removal under Condition-4 of the loading which was double the standard loading. The aeration zone located after the 2nd anaerobic zone had high treatment capacity. More than 90% of COD in the 2nd anaerobic zone effluent was removed through the aeration zone regardless of the BOD loading. However, a catastrophic decrease in COD reduction rate occurred in Condition-4. The BOD loading in Condition-3, which was 1.5 times the standard loading seemed to be the critical condition for treatment. Within 10 days of adding viruses to the apparatus, the virus concentration in each zone of the system became almost steady. Reductions of T2 phage and poliovirus I with varying BOD loadings are shown in Figure 1. The pattern of virus reduction through the system was almost the same as that of COD reduction. Under the standard loading of the Johkasou used here (O.076kgBOD/m 3/day), T2 phage reduction rates which were calculated by comparing titres of the raw influent with titres in the outlet of the 1st anaerobic zone, of the 2nd anaerobic zone and of the aeration zone equipped with contact media were 76%. 82% and 97% respectively. Percent reductions during the 2nd anaerobic zone alone and during the aeration zone alone were 25% and 81% respectively. When the BOD loadings became I.S or more of the standard, T2 phage reduction rates in the aeration process decreased to below 70%.

189

Domestic wastewater treatment system named Johkasou

RellOval rates(%)

RellOval rates(%)

1

1

~ ~.d'; -

a

0.051 0.076 0.114 0.152

~

kgBOO/. 3 ·day 0.051 0.076 0.114 0.152

b

1st aeration 2nd anaerobic anaerobic zone zone zone

aeration 2nd 1st anaerobic anaerobic zone zone zone

Figure I. Removal rates of 1'2 phage (a) and poliovirus I (b) through the system.

Poliovirus I reduction under the standard condition was 69% during the retention in the first anaerobic process and 78% to the outlet of the second anaerobic zone (26% in the second anaerobic zone alone). Overall removal through the total system was 98% (92% in the aeration zone alone) (Figure 2). When the BOD loading was twice the standard, poliovirus I decreased by 53% in the first anaerobic zone and by 57% to the end of the second anaerobic zone as compared with the titre of raw influent (12% in the second anaerobic zone alone). The overall virus removal through the system was 33% (65% in the final aeration zone alone). The results of experiments on coxsackievirus B3 removal were similar to that with T2 phage and poliovirus I. Under standard condition, coxsackievirus B3 decreased by 73% during the 1st anaerobic process and by 81 % to the end of the 2nd anaerobic zone as compared with the titre of raw influent (28% in the 2nd anaerobic zone alone). Overall removal rate through the system was 93% (91% in the aeration zone alone). Virus removal by the system was not affected by virus concentrations between lx10 2 PFUIL and 7.6x105 PFUIL in the influent. R~val

1

rates(%)

1tg8OO/.3·l!ay o 0.051 EI 0.076 D 0.114 .. 0.152

1st 2nd aeration anaerobic anaerobic zone zone zone Figure 2. Removal rates of poliovirus I in each component pan.

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M.KANEKO

DISCUSSION The virus removal rate found in the first anaerobic zone was high. When the virus removal potential in the first anaerobic zone deteriorated, the virus concentration of the effluent became high. However, the highest percentage virus reduction was obtained in the aeration zone equipped with contact media. Therefore, the virus concentration in the outlet water from the system depended on the virus removal capacity of the aeration zone. Inactivation activity of microorganisms attached on the contact media in the aeration zone can be estimated as follows. If it is assumed that the water stream in each zone is completely mixed and virus reduction is indicated by equation (I), where N, k and t indicate viral counts, rate constant and time respectively, the input-output balance of viruses in each zone is expressed by equation (2), where Q and V indicate the influent flow(Uh) and the volume of each zone (L) respectively. dN/dt= kN

(I)

VxdN/dt = Q(No-N)-KNV

(2)

Equation (3) is introduced by integration of equation (2), where T is a retention time (h). N = [No/(kT+I)J[I-exp-(IIT+k)t]

(3)

If Iff>-k, N converges into the value expressed by equation (4) in course of time.

(4)

N = No/(kT+I) If IIT+k=O, N=Noxlff

(5)

The rate constant k, which indicates the inactivation ability of microorganisms in each zone, can be calculated by equation (4) or (5). Values of k calculated from the data on the virus removal in the aeration zone are shown in Table 2. Table 2. Inactivation rate constant (k)

t

Condition g BOO/dal, Flow rate (m /h)t k (lib) T2 phage k(IIb)Polio I total volume ofthe modellO.9L

0.48 31.1 0.193

0477

2 0.72

20.7

0.193 0.538

3 1.08 13.8

0071 0181

4 1.44 10.4 0.045 0183

It can be seen in the table that the virus removal potential is influenced by the inactivation activity of BOD. degrading microorganisms in the zone along with the retention time of viruses in the same zone. The higher the BOD loadings, the lower the values of k. Higher BOD loadings than the standard condition would result in lower virus removal activity of microorganisms in the system and poorer effluent viral quality. Results in experiments using T2 phage were similar to those obtained using poliovirus and coxsackievirus. Therefore, T2 phage could be used as the indicator virus for enteroviruses in evaluating the virus removal activity of Johkasou or similar small waste treatment plants (Hanna et al.. 1995). CONCLUSION Virus removal by Johkasou, a small device for treatment of domestic wastewater, was investigated using a scale model. The Johkasou could remove more than 97% of viruses (T2 phage, poliovirus and coxsackievirus) in raw inlet water under standard BOD loading of 0.076 kgBOD/m 3/day. Virus removal

Domestic wastewater lreatment system named Johkasou

191

efficiency in a process depended on the retention time of viruses in the process and the virus inactivation activity of microorganisms living in the process.

REFERENCES Hanna. K. M., Kellam. J. Land Soadman G. D. (1995). On-site aerobic package treatment systems. Wal. Res., 29, 2530-2540. Japan Education Center of Environmental Sanitation (JECES) (1994). Johkasou Sys/~m for Tr~a/mrn/ ofDomes/ic Wastewat,r.