Pasteurization of raw and digested sludge

Water Research Pergamon Press 1972. Vol. 6, pp. 561-563. Printed in Great Britain

PASTEURIZATION OF RAW AND DIGESTED SLUDGE G . KUGEL Niersverband, Postfach 529, D-406 Viersen, F R G

IF A large quantity of sludge has to be delivered day by day without storage for some months it is necessary to render it hygienic to handle before irrigating pasture land. TRI~aEL (1961, 1968, 1969) described installations for the thermal treatment of liquid sludge. Nowadays this can be done without difficulty. FIGURE 1 shows the flow of sludge and the main installations for a discontinuous procedure; the double set allows however a semi-continuous discharge of sludge if small quantities are to be treated. Schlamm zulouf ~--

5

7"~ $

5~j~l.~ /Schlommf~Jllstond.~

L_

2L~

5

___ ,u-

I j

n I I

___ I ~o-I

~---m----'~ I ,

~- I , ~[ L . . ( ~ ,

~

L J_'.

I

EIT o,

[I

_L ', I (t~.. J

¢'~1

~

,J

-'4

1 ....

-- -,,-- Schlommablauf

FIo. 1. Pasteurization plant, discontinuous operation. la, l b pasteurization reactor 2 steam boiler 3 sludge pump (input) 4 sludge pump (rccircle) 5 air, vapours outlet.

FIGURE 2 shows the flow diagram of the pasteurization installations at our biggest plant (700,000 population equivalent) is based on a continuous process of two-step heating (reactors No. 2 and 4) and two-step recooling (reactor No. 5). For the economical use of steam efficient heat recovers recuperation combined with preheating is used. At a vacuum pressure of 0.1 atm vapours are returned from the first reactor No. 5 to the reactor No. 2. This pasteurization plant at Crruppenklirwerk I, MSnchengladbach-Neuwerk, is now charged with sludge continuously at 28 m s h-~. To use steam most economically multiple heat recovery and sludge preheating is required. There is a limit to reliability, maintenance and the cost of installation of the system. The reliability R= of a multiple system, especially in case of series-connexion, decreases quickly:

Rm ~

r t . r 2 ......

ri ......

0
1.

rm ~

~r rt l=!

562

G. KUGEL ! :- . . . . . . .

r-~l

!i---~

'

~--i

!

I

I

I

~1 4 I

~

I

i

!

It

I_', III i

'I,

,le'-.' .

l~ I41

zu den V o k u u r n p u m . ~ L

14

:

M,°,° ~"Y 1 r-

1

"~',r ,

,-~ ..... ]

45.

I]

L _ ,,....~'~0,057,

I

r3~,l

, i

Y~3o°i I

l^r=o

I

D'J f-.-n

rL_

35~:

....

]l

i

~

I

, .

, ~

',~rJ

I

~

'

tt

14

zum Tankwagen

r ....

I

FIG. 2. Pasteurization plant continuous operation (Gruppenklarwerk I, Niersverband). (1) digested sludge, thickened (2) preheating reactor (3) (4) pasteurization reactor, detention chamber included (5) cooling reactors (6) condensor (7) pasteurized sludge (8) pumps. Schlamm = sludge, HeiBdampf = steam, Br~den = vapours, Wasser = water.

The system reliability can be improved by higher reliability of each element as well as by redundant stages, i.e. by a combination of series and parallel connexion:

•

-gw;-q

~

•

..

°

°

.

.....

R=~[l--~(I--r,~)] i=l

°

•

.-i

°

1 .

0
=!

Both methods, either improvement or redundancy, cost money. The same reliability aspects have to be considered also in case of other ways of sludge treatment and disposal. The newest pasteurization installation of Niersverhand is built at Gruppenkl~rwerk Nette and charged with raw sludge at 10 m 3 h-1. The thermal process is similar to the scheme shown in Fxo. 2 but without the second step of recooling. Here the warm sludge is discharged into steel storage tanks at about 40°C, where the temperature may fall to 30 ° or 35°C.

Pasteurization of Raw and Digested Sludge

563

After 2750 operation cycles in 1970 the performance was sufficient to be described by the following typical figures: steam

fuel operation cost fuel, electricity water chemicals (water treatment) maintenance, operator repair, inspection management (10 %) total operation cost

78 kg m-3 raw sludge 5"5 l.m -3 0.68 DM 0-07 DM 0.14 DM 0.49 DM 0.29 DM 1.67 DM 0.17 DM 1.84 DM

m-3 m-3 m -3 m-3 m-3 m-3 m -3 m-3.

The total cost of installation, storage tanks included, was about 550,000 DM in 1969. REFERENCES HOFMANNW. 0968) Zuverldssigke# yon MeJ~, Steuero, Regel- und Sicherheitssystemen. Verlag K. Thieme, Mfinchen. KUOEL(3. (1971) Pasteurisierung yon Roh- und Faulschlamm. Abwassertagung, ATV, Essen. TRmBEL W. (1961) Erfahrungen mit der Schlammpasteurisierung Technik und Wirtschaftlichkeit. 1AM-Informatiomblatt Nr. 30. TgmBELW. 0968) MSglichkeit der landwirtschaftlichen Verwertung yon Faulschlamm. Europdisches Abwassersyraposium, Mfinchen. TmEB~L W. (1969) Pasteurisierung der Klarschlamme. lAM-KongreJ3, Basel.