Effect of physico-chemical

pretreatment on the removal

efficiency of horizontal

subsurface-flow constructed

wetlandswetlands

Aracelly Caselles-Osorio and Joan Garcia (2006).

Review and Presentation by:

MUNANURA JAMES.

REG: NO: 2011/HD13/4234X

STUDENT NO: 211017023

APRIL 2013

INTRODUCTION

• Application of (SSF

CWs) for sanitation

of urban

wastewaters has

proven their proven their

feasibility for

removing organic

matter, nitrogen and

other contaminants.

INTRODUCTION

• Effect of a physico-chemical pretreatment on

contaminant removal efficiency in two

experimental horizontal subsurface- flow

constructed wetlands (SSF CWs).constructed wetlands (SSF CWs).

• One SSF CW was fed with settled urban

wastewater.

• Other with the same wastewater after it had

undergone a physico-chemical pretreatment.

INTRODUCTION

• The efficiency of the two systems was tested

under different conditions.

• At the end of the experiments, the hydraulic

conductivity was measured to determine how conductivity was measured to determine how

the physico-chemical treatment helped to

maintain it.

PROBLEM STATEMENT

• One of the problems affecting the efficiency of SSF CW efficiency is the progressive clogging that that occurs near the inlet as a result of solids entrapment and sedimentation, bio-film growth and chemical precipitation.growth and chemical precipitation.

• To prevent clogging use of intensive pretreatment processes would improve removal efficiency. (Coagulation, Floculation, Clarification)

OBJECTIVE

• To evaluate the effect of a physico-chemical

pretreatment on the effluent quality of SSF

CWs.

MATERIALS AND METHODS

• EXPERIMENTAL SSF CW.

• The two SSF CWs consisted of plasticContainers (0.93 m long, 0.59 m wide and 0.52m deep) filled with gravel extracted from nearm deep) filled with gravel extracted from nearthe outlet of one bed of a pilot SSF CWsystem.

• Each container had a drainage pipe located on the bottom of the effluent side. The bottom was flat.

MATERIALS AND METHODS

• The experimental SSF CWs were planted in June 2004 with developed rhizomes of common reed (Phragmites australis).

INFLUENTS AND FEEDING STRATEGY.

Both SSF CWs were fed daily in batch mode.• Both SSF CWs were fed daily in batch mode.

• One SSF CW was fed with primary settled wastewater (known as PE), and the other with the same settled wastewater (known as PTPE), after it had undergone a physico-chemical pretreatment.

MATERIALS AND METHODS.

• INFLUENTS AND FEEDING STRATEGY.

• This feeding strategy was used instead of

continuous operation to avoid solids

sedimentation and adsorption onto the walls sedimentation and adsorption onto the walls

of tanks and pipes.

• Batch operation, is good for comparison of the

performance of the two experimental SSF

CWs.

MATERIALS AND METHODS

• Hydraulic conductivity tests (HCTs).

• HCTs were carried out near the inlet of each

SSF CW (in exactly the same position) in order

to examine the effect of the pretreatment onto examine the effect of the pretreatment on

the hydraulic conductivity of the granular

medium.

RESULTS AND DISCUSSION

• The waste water Temperature, Turbidity,

Electrical conductivity and evapotranspitation

were measured.

• Temp = Similar.• Temp = Similar.

• Turbidity reduced by physico-chemical pre-

treatment.

• As HRT increases the turbidity increases i.e. (2

day HRT).

RESULTS AND DISCUSSION.

RESULTS AND DISCUSSION

• EXPLANATION FOR HIGHER TURBIDITY WITH

HIGH (HRT).

• Precipitation of CaCO3 and other carbonate

salts. salts.

• Formation of elemental sulphur from H2S.

• Presence of Sulphate reducing bacteria.

RESULTS AND DISCUSSION

• ELECTRICAL CONDUCTIVITY.

• In general electrical conductivity slightly

higher in effluent than influents. Probably due

evapotranspiration.evapotranspiration.

RESULTS AND DISCUSSION

• (COD) Conc.

Changes.

COD CONC. CHANGES

• Influent PTPE COD < Influent PE COD. Due to physico-chemical treatment.

• Effluent Conc. COD PTPE < Effluent Conc. COD PE. When surface loading was very high in both SSF.

Global effluent COD conc. Differences between • Global effluent COD conc. Differences between the two SSF CWs were statistically significant.

• COD percentage removal efficiencies and COD mass surface removal rates were higher in the PE SSF CW due to the greater influent COD concentration.

COD CONC. CHANGES.

• The trend shows that the efficiency of SSF CW

systems cannot be evaluated using just the

removal percentage or the mass surface

removal rate, because it depends on the removal rate, because it depends on the

influent properties and not on the effluent

quality.

CHANGES IN NH3 Nitrogen.

CHANGES IN SULPHATE CONC.

CONCLUSION

• Use of a physico-chemical treatment as a preliminary step for SSF CWs did not improve the quality of the effluents in terms of turbidity, COD and ammonia N.

• After 8 months of operation the SSF CW fed with • After 8 months of operation the SSF CW fed with PE had a lower hydraulic conductivity than the SSF CW fed with PTPE.

• It was estimated that the physico-chemical pretreatment allowed to extend the life-span of the SSF in approximately 10 years in comparison to the SSF fed with settled wastewater.

CONCLUSION

• Physico-chemical treatment has certain

requirements that can make this process

unsuitable in the context of constructed

wetlands technology:wetlands technology:

�Cost of coagulants.

�Energy for adding and mixing coagulants.

�Sludge handling.

CONCLUSION

• Physicochemical pretreatment can

significantly extend the life-span of the SSF

CWs and at the same time be economically

viable.viable.

• One other possible advantage of the physico-

chemical pretreatment could be the additional

removal of phosphorus.

THANK YOU.