This booklet focuses on research workfunded by a grant program of Rhodelsland Department of EnvironmentalManagement pursuant to the Hazard-ous Waste Reduction, Recycling, andTreatment Research and Demonstra-tion Act of 1986(Chapter23- 19.10 ofthe Rhode lsland General Laws)

This booklet is published by the Rhode IslandDepartment of Environmental Management,Office of Environmental Coordination, andthe Water Resource Center of the Universityof Rhode Island.

The contents of this publication do. not necessarilyreflect the views and policies of the RI Departmentof Environmental Management and University ofRhode Island, nor does the mention of trade namesor commercial products constitute their endorsementby these two agencies.

ELECTROFLOTATION

Prepared by

Calvin P.C. Poon, DirectorWater Resources Center

U N I V E R S I T Y O F R H O D E I S L A N D

K I N G S T O N , R I 0 2 8 8 1

Fundina Program Objective:

Promote the research development,and demonstration of methods andtechnologies which have the potential toreduce the volume and/or toxicity ofhazardous waste generated in RhodeIsland.

FOUR STEPS OF ELIGIBLE PROJECTS

l Feasibi l i ty Studies

l Pro jec t Des ign

l Construct ion of Demonstrat ion Faci l i t ies

l Evaluation of Facility Effectiveness andAssessment of Applicability to Other Facilities

s h o p W a t e r Total Ni Cu Zn Pb Cr

size U s e C y a n i d ega l /d lb/d lb/d

SMALLrinse 5,830water

dumps 20

MEDIUMrinse 35,720water

dumps 130

LARGErinse 183,140water

dumps 660

0.39 0.53

0.11 -

2.40 3.30

0.66 0.03

12.30 16.90

3.40 0.11

0.40

0.05

2.48

0.27

12.70

1.41

0.14 0.008

0.03 -

0.86 0.046

0.19 0.002

4.41 0.240

0.93 0.010

0.01

I

0.061

0.310

Source : Summary Report, Metal Finishing Industry, EnvironmentalAssistance project, Oct. 1980 Manufacturing Jewelers and Silversmiths ofAmerica Inc. and the Rhode Island Department of Economic Development.

WATERANDWASTEREDUCTION

• Counter - Current Rinse

l Fog - Spray Rinse

l Flow Controlleruse either flowrestrictor orconductivitycontroller

l Agitatorair agitatorincreases rinsingefficiency

l Rinse Water Reuserinse water outputfrom one rinse tankis used as inputto rinsing tanksat other locationsin the process line

l Reduction in water andsewer use charges

l Reduction of process chemicalslost to sewer by dragout

l Reduction in capital andoperating costs of waste treatment

l Reduction in sludge quantitiesand disposal cost.

6 STEPS

1. Identify and quantify sourcesof pollution,

2. Non - polluting chemicalssubstitution.

3. Waste stream segregation:CN bearing, acid/alkali bearing,and chrome bearing.

4. Reduce dragout by using wettingagents, sufficient rack andbarrel drain time.

5. Use dragout and/or fog spraytanks to concentrate the solution.

6. Return concentrated dragoutsto plating and cleaning baths.

Small tomediumshops up t o

184,000gpd

I

Largeshop

Adequate reactor mixingGood ventilationFree chlorine monitoring forcontrolpH monitoring for control

Adequate reactor mixingpH adjustment

Coagulant and/or polymermay be needed

Coagulant and / or polymermay be neededNot cost-effective for smallto medium shops

Source : Summary Report, Metal Finishing Industry, Environmental AssistanceProject, Oct. 1980. Manufacturing Jewelers and Silversmiths of America, Inc.and the Rhode Island Department of Economic Development.

1. PROVIDENCE METHOD

l Use multiple “trickling” dragout tanksl Final rinse discharged to sewerl Intermediate tank effluent to holding or plating tank

3. SULFIDE PRECIPITATION

l Use soluble sulfide (Na-sulfide or hydrosulfide)l Use insoluble sulfide (ferrous sulfide)l Precipitate metals and reduce Cr(+6)l Advantages include minimal interference by chelating

agents and perform well on many complexedheavy metals.

ELECTROFLOTATION

WHAT DOES IT DO ?

MAJOR TREATMENT SYSTEM COMPONENTS

1. Set electrode spacing at 3 to 4 cm

2. Start the system as a batch process with 0.01 - 0.02 amp / sq cmcurrent density (4 - Volt minimum), wastewater ( rinsing effluent)depth at 20 to 25 - cm, and 60 minutes treatment for Ni.75 minutes for Cu - CN, 75 minutes for Zn - Pb.

3. At the end of the batch treatment, turn on the rock saltsolution recirculation pump to provide a 20 - minute hydraulicretention time. Concurrently, the wastewater pump is turnedon to provide a hydraulic retention indicated in step 2 above.

4. Monitoring Requirements:

Operation:pH in reactor (twice a day)Effluent residual chlorine (once a day)Effluent residual chloride (once a week)

Effluent Quality:

pHMetal concentrationCN concentration(as required by regulating agency)

ELECTROFLOTATION PROTOTYPE SYSTEM DESIGN

Five gallon per minute flow rate(one production line for a small shop)

Electroflotation tank, polypropylene,custom - built 375 gallon capacity

Anode, platinum clad columbium screen,4 tabs, 2093 square inches

Cathode, stainless steel screen, 4 tabs

Rock salt solution reservoir, 55 - gal.

Sand filter, 22 - in dia. 3 ft deeppolyethylene tank

Automatic scum skimmer, custom - built 1,250

Metering pumps for wastewater androck salt solution

Power supply and regulator

Installation cost, 25 % 3,680

1990 cost

$2,900

7,500(10 % discountfor over 1000 in )

1,620

100

200

700

350

Daily Avg.Max.l-day

composite 10 - day

Cd (T) 0.11 mg 0.07 mg/l

Cr (T) 2.77 1.71

Cu (T) 1.20 1.20

Cn (T) 0.58 0.58

Pb (T) 0.60 0.40

Hg (T) 0.005 0.005

Ni (T) 1.61 1.62

Ag (T) 0.43 0.24

Zn (T) 2.61 1.48

TTO 2.13 2.13

pH 5 - 10, standard unit

4-Hourcomposite

sample

0.05 - 0.14 mg/l

0.02 - 0.03 mg/l

0.16 - 0.34 mg/l

0.19 - 0.35 mg/l

0.23 - 0.52 mg/l

7.8 - 10.6

I

Electroflotationsystem

(2x prototype units)10 gal/min

Installedcost (1990) : $36,800

Operating andmaintenencecost : 7,66O/yr

Spacerequirement : 100 sq ft

Operationalskillrequirement low

The cost advantageof the electroflotationsystem is greatlyreduced if wastewater(rinsing effluent of aplating shop) doesnot contain CN.

Conventional system(CN - oxidation, Alkaline

precipitation, flocculation-clarification units)

10 gal/min

$68,820

13,68O/yr

500 sq ft

medium