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Wat. Sci. Tech. Vol. 31, No. 3-4, pp. 341-344,1995.Copyright© 19951AWQ

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APPLICATION OF DISSOLVED AIRFLOTATION FOR TREATMENT OFWASTEWATER FROM MEATPROCESSING INDUSTRY

J. Wasowski

The Water Supply and Hydraulic Institute of Warsaw University ofTechnology,20 Nowowiejska Str., 00-653 Warsaw, Poland

ABSTRACT

The paper concerns the application of dissolved air flotation for treatment of waste water from the meatprocessing industry. The main aim of the study was identification of the flotation mechanism aided by thecoagulation in the layouts with and without recycling, and finding and defining the role of the technologicalfactors influencing flotability of pollutants found in the given waste waters. The results of the studies,supported by the mathematical analysis, form the basis of rational design and conduction of flotation inpractice.

KEYWORDS

Dissolved air flotation; meat processing industry; waste water treatment.

THE AIM OF THE STUDIES

The studies were aimed at identification of dissolved air flotation mechanisms with regard to treatment ofwaste waters from meat processing industries. The studies were also aimed at finding and determining therole of relevant technological factors, facilitating adoption of a rational basis for design and operation of theflotation process in practice.

THE METHOD OF CONDUCTING THE STUDIES

The process of dissolved air flotation was carried on a laboratory scale in static conditions and using theexperimental apparatus shown in Fig. 1.

Flotation was studied in the following layouts:

without recycling and without use of reagents;without recycling and using reagents;with recycling and using reagents.

341

342 J. WASOWSKI

During the flotation process the following were used as reagents:

mineral coagulants, i.e. aluminium sulphate representing the group of hydrolyzing coagulantsand magnesium chloride representing the group of electrolyte coagulants,

organic coagulant, i.e, lignosulphonate (waste product during the production of cellulose usingthe sulphite method),

factors influencing the reaction environment, i.e. calcium hydroxide and sulphuric acid.

The exemplary results of those tests in regard to turbidity of waste waters are shown in Fig. 2.

The studies on dissolved air flotation were conducted to assess the influence of basic physical parameters ofthe flotation process, i.e. the amount of released air (A) dependent on the saturation pressure (p) in saturationchamber, degree of recycling (R), initial suspended solids concentration (Si)' and the average rate of ascent(v) understood as the ratio of chamber height (H) to the flotation time in the chamber (t), on flotation ofpollutants from the waste waters in studied flotation layouts.

3 4

67

8

9

Fig. I. Diagram of the layout of the investigative plant for the dissolved air flotation process.I. Pressurised saturation chamber (V =5 dm 3, ts =5 min, p = 0.2-0.5 MPa)

2. Manometer3. Sewage inflow

4. Air outflow5. Rotameter

6. Compressor7. Flotation chamber (V = Idm3, h = 45 em, d = 5 em)

8. Point of sewage sampling9. Nozzle (d=O.5 mm)

10. Valve

Dissol ved air flotation 343

960I-Z

L:::.J 50

~ 40'6.s... 30::l-C 20::l

"0iii 10Q)

a:0

3

100 200 300 400 500 500 700 800

Initial turbidity1.-900 (NTU]2.-1000(NTU]3.-1200(NTU]

pH in the point of min.1. - pH=6.12. - pH=6.33. - pH=6.3

Dose of Al2 (504)3

[mgfdm3]

9 120I-

6100

>- 80-'6ii

60...::l

C 40::l

"020·iii

Q)

a:0

500 1000 1500 2000 2500

Initial turbidity1.-900 (NTU]2.-1000(NTU]3.-1200(NTU]

pH in the point ofmin.1. - pH=11.6, 1500mg Ca(OH)z/dm3

2. - pH=11.0, 1350 mg Ca(OH)2/dm33. - pH=I1.3, 1000mg Ca(OH)idm3

Dose of Mg Cl2

[mg/dm3]

Initial turbidity1.-900 (NTU]2.-1000[NTU]!~ 3.-1200(NTU]

~ pH in the point ofmin.1. - pH=3.0, 0.5 cnr' H1SOidm

3

2. - pH=3.1, 0.6 em' H1S04/dm3

-w)--"----_-6 3. - pH=2.8, 0.7 crrr' H1S04/dm3

50 100 150 200 250 300 350 400 450 500

....l----.--,--,...--,--,.---,--r---,--,.-----.----1~ Dose of Ii9nosu Iphonater- /dm3J

80

709I- 60

650

~'6 40is....i! 30

C20::l

"0IIIQ) 10a:

0

Fig. 2. Relationship between the treated sewage turbidity and the dose of the coagulants.

344

CONCLUSIONS

J. WASOWSKI

The studies carried out allowed formulation of the following conclusions.

The course of the dissolved air flotation process in treating the waste waters from meat processing industrydepends mainly on:

volume of air corresponding to the unit mass of removed suspended solids, i.e. the value of NSiratio;doses and types of reagents assisting the flotation,the flotation layout.

In the studied flotation layouts the content of suspended solids in treated sewage (Se) decreasesexponentially (y =ax-b) with the increase of NSi ratio (Fig. 3).

A/Si[Cm

3/mgJ

0,025

0,020

0,015

0,010

0,005

3

-'----r-r--,----r-...,.......-.------,r---,----.,.-...,.......---:=-l~ Se100 200 300 400 500 600 700 800 900 1000 [mg/dm3]

Fig. 3. Relationship between content of suspended solids Se in the sewage after flotation and the value of AlS i ratiofor different reagents and flotation layouts (according to the general formula y =ax 'Il).

I. no reagents and no recycling: y = 26864x·2.1385

2. with A12(S04)3 and no recycling: y =O.0227x·O.12553. with Al2(S04)3 with recycling: y =2.33lx·1.l21O

4. with MgCl2 no recyclin: y =O.025lx-O·2750

5. with MgCl2 with recycling: y = O.0376x·0.3627

6. lignosulphonate no recycling: y = O.026lx·0.10557.lignosulphonate with recycling: y =566.3x·1.8062