~!ldrotech,9:ical ConstTTtction. 1/~1. 3~, No. 7. 200(]

A SETTLER FOR CLARIFYING WATER

D. M. M u r a d o v

Existing settlers are either rectilinear or radial typ(,s. A r~ulial settler can be used for low flow rates, and the number of them can be increased to handle higher rates. Th(,v rem<~w~ the suspensates a~ the same time ~s providing clarification, i.e., they operate continuously, but the clarification in one does not exceed 50-60%.

A rectilinear settler is designed fbr period hydrauli(" ~'timination of the sludge if there is an adequate difference in level between the settler and the sludge discharge. If th(,re is no such facility, it may be built directly on the ground without reinforcement of the bo t tom and the sides for th(, lmrp()se of removing the deposited suspensates, which in the main are eliminated by a foa t ing collector. A rectilim~ar s('ttt('r with hydraulic sludge removal is designed with a reinforced floor and nufltisection walk~ in order to (:lari~" the, w;~ter in an ongoing f~shion while the sludge is being w~ushed out in one section. To eliminate the sludge in su('h a s(,tth,r may require a considerable amount of water. The clarification in such a settler does not exceed 40-50%.

These settlers are expensive to build and require manipulat ion gates for removing the sludge. A rectilinear settler in which the sludge is removed by a collector may b(, titt(,(l with sludge collectors, and it may not be very expensive to build, but its operating costs are high on ~u'('ount of the need to service the collector. The clarification does not exceed 20-25%.

To eliminate these detbcts, I have designed an effi('i(,nt s(,tth,r in which the length is less titan the width att(t the depth is large, i.e., it takes the form of a rectangular pond.

This settler can perform tim following: 1) clarifv cloudy water with any degree of cloudim,ss to over 90% and give an ou tpu t cloudiness of less than

1 kg/m3: 2) it can remove the sludge hy(traulically either conti lmously or periodically wi thout shutt ing down the

clarification and which can operate with sludge concentrations up to 50%. which means that less than :3(7o of the clarified water is needed to eliminate the slu(tge. There is hardl.v any need for staffing:

3) a single settler without sections or gates can 1),, us(,d tbr any water flow: and 4) the settler t)~sin can be built wi thout wall reintbrccmcnt, i.e., directly in the ground, which is quite cheap

to build. My settler ht~s a triangular basin with water depth not less than 8-9 m. This t r iangular section is built

trapezoidal (htring co~struction with a b o t t o m of width not h,ss than 2 m, in which the sludge remover is mounted (my design). The trapezoidal section after commissionin~ is conv(,rtc~t to triangular by the sliding of the sludge towards the sludge pump. The sides of the tr iangular section arc built with m ~> t.5 up to rn = 3 in accordance with the grain-size composit ion of the turbidity: For predominant sandy fractions, rn/> 1.5. while for muddy ones ra ~< 3. The basin has end wails of identical s t ructure.

This settler ha,s a deposition path length related to the d(,pth and structure of the wails ranging from 25 to 100 m.

The width is related to the flow rate and the degre~ ~ of ('larification required and can range from 40 to 200 m or more. The water is admit ted from a prel iminary chamber through the inlet wall and passing tlu'ough guide rods, which provides for uniform inlet and increases the path length in the inlet layer, which improves the clarification.

The depth of the pond is c(nnparatively great by comparison with that, of the moving thin layer, which is the main reason for the rapid sedimentation, The clarified water is drained from the pond via an ordinary pipe.

The sludge is removed continuously or periodically by the sludge remover, which has pressurized nozzles and is installed on the horizontal bo t tom as a telescopic perforat(~d pipe. The suction holes are fbrlned in the lower par t of the tube at 45 ° for the first hole and at the top of the tul)~, for the subsequent ones.

The sludge inlet speed at the first hole is not less than 1 m/see, while the inlet speeds at the subsequent ones are up to 3-4 m/sec. The distances between these holes are related to the pond size and range from 2 to 5 m. The

Translated from Gidrotekhnicheskoe Stroitel 'stvo. No. 7, pp. 13-14, July, 2000.

336 0018-8220/00/3407-0336525.00 @2001 Kluwer Acadenf ic /P lemun Publishers

TABLE 1.

O s /Zin, Il l Uia,

1 0.(59

2 0.79

3 0.93

4 i .22,

q in ,

m/~ec liter/sec

o .? I0

2.4 10

2.6 10

3.0 iO

din, /sl,. II1

i l l l n

170 2.3

70 2.3

7O 2.3

(5.5 2.S

(/sp, (tsp* l l l l l t

liter/sec 180.5

50 170

60 s a m e

7 0 s a m e

2 4 5 - 6 150

233

Usp, ]l,w! I l l

Ill/S(?(~

2.20 0.10

2.66 0.14

3.10 0.20

3.50 2.20

y~.hw = 3.50

Working fbrmul~s

t ' in = ,tlX/2.(]h,[~ f o r a l l h o l e s ,

we take Ii = 0.6. and dmn

h . . . . I -/ ' 'e d29 for l =2 .3 and

2 hw ~ 0.00;~5 d fi)r ,\ = 0.03

perforated par t of tile pipe is .joined to a comlecting par t essentially at the middle of tile pond and runs under the pre l iminary ehanll~er to the sludge discharge point. The sludge is discharged on account of tile differences in water level be tween tile pond and tile discharge point. If there is no such level ditt~rence, or even tlle sludge discharge point is above tile water in the basin, the sludge, is ba,~ically removed by a sludge p m n p installed at tile end of tile sludge remover, which is driven by water and requires a supI)ly of t00 liter/see and a head of not less than 20 m. The suc t ion holes in the sludge remover may become choked or blocked. To prevent this. each hole is fitted with a moni tor nozzle supplied with pressurized water. The head at the nozzle should be not less than lt) m, while tile flow to each nozzle should be not less than 1-2 liter/see. These nozzles are installed at the ~uxis of the tube for the first hole a n d at 30 ° to the generator of tile tube tbr the rest, subject to the condit ion that the jet fi'om the nozzle enters completely into the hole.

At the end of tile sludge remover tlwre is a mamla l slide valve for opening and closing it. A good idea of tile design is provided by tile following. To handle a flow- rate of turb id water of 5 nla/See

and wi th a design turbidi ty of 10 k g / m a, one can ob ta in a lnluxilnllln clarification of 90% with an output of sludge % = 5- 10- 0.90 = 45 kg/sec, in which the sludge contains 30% solid, and therefin'e q~ = 45 : 0.3 = 150 liter/see. W i t h a pool wid th of 40 m, tile sludge flow per each meter of the width is qw = 150 : 40 = a.7,5 liter/see. The horizontal floor of the settler is about 14 in long, anti tile distances between the suction holes are l ~ 2.3 m, there being seven of thenl. In the connecting par t of tile sludge remover, there are three suction holes on each side of tile middle of tile settler, and one hole in the connect ing pipe. The end walls with a length of 14 m mean tha t the first suction holes will d raw sludge with a flow rate of % = 14 • ;/.75 ~ 50 l i ter /see from the ends. And then the other holes will suck off the remain ing 5(} liter/see, i.e., 10 liter/see in e~mh of the middle holes.

Table 1 gives hydraulic calculations on the sludge remow'r with an inlet speed of sludge at the first hole of not less thml 2 m/see.

W i t h tile existing difference ill levels, dm eommcting part of the sludge remover passes raider the prel iminary chamber. Safe filling of the sett ler ba,Mn on s tar tup is provided by an inlet pipe with phlg in the preliminary chamber, which is jo ined to the connect ing t)art of the sludge remover.

T h e sludge remover is fitted with nozzles for prevent ive flushing of the suct ion hol(~ to eliminate blocki~g. Ial the first holes, the nozzles are of diameter 30 thin, while they are of diameter 15 m m tbr the InkklIe ones. W i t h a m i n i m u m head H = 10 m tbr tile pressurized water, the first suction holes will receive a flow rate q = 9 l i ter /see with speed v ~ 12.5 m/sec, while tile middle ones will receive q ~ 2.2 liter/sec with the same speed. These flow rates and speeds provide tbr flushing tile holes (:lear if they become blocked.

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