Hi friend! What kind of heavy metals are you working? Pb, Cd, Zn, etc.? The most inexpensive way is upping the soil pH to 6,0 - 7,0. In this range, the most part of heavy metals are not unavailable to plants.

Biosorption is now an emerging tool for treatment of heavy metals in which most of the metals are removed. The selection of material depends on adsorption capacity of material for that metal. For example Syzygium cumini seed & barks are best biosorbent for Chromium (VI)

I want to treat Pb or Cd from groundwater using in-situ treatment. the material must be in ground for years.

Sorption methods are usually the methods of choice in case of larger water amounts with low-concentrated pollutants. Sorption material (a lot of described in research material) of high surface must be placed with its three-dimensional structure inside the water or, better, in flow-through units of permanent working or into the line in case of water pumping from the reservoir. Biofilm formation could be a problem over long time. A good variant is electrochemically supported adsorption/desorption but this field is not yet completed and still under research due to several problems such as stability of sorption material.

but come to think of it, while considering environmental sustainability, are we considering cost as the main concern or how sustainable the action will be?

because I am of the idea that this cost thing should not be so emphasized while trying to achieve that ultimate goal of sustainability. 

the watch word should be how green is the technology applied ,,,,, and something like that

but come to think of it, while considering environmental sustainability, are we considering cost as the main concern or how sustainable the action will be?

because I am of the idea that this cost thing should not be so emphasized while trying to achieve that ultimate goal of sustainability. 

the watch word should be how green is the technology applied ,,,,, and something like that

but come to think of it, while considering environmental sustainability, are we considering cost as the main concern or how sustainable the action will be?

because I am of the idea that this cost thing should not be so emphasized while trying to achieve that ultimate goal of sustainability. 

the watch word should be how green is the technology applied ,,,,, and something like that

Dear Charles,

In every engineering projects, cost play an special role that must be regarding.

The most effective means that is cost effective, environmentally friendly and aesthetically pleasing and solar driven is the use of plants( Phytoremediation)

The short answer is that there isn't a short answer. There are a number of methods which have been raised here, all of which have potential. Without knowing the general water chemistry, it's also difficult to make a recommendation.

There's a growing feeling that the term "heavy metals" should not be used. See the attached reference (Duffus, J H. ""Heavy Metals" - a Meaningless Term? (Iupac Technical Report)." Pure and Applied Chemistry 74, no. 5 (2002): 793-807.) for reasons why. There is no consistent definition and the range of metals which get this description are going to have quite different chemical behaviours in different solutions.

http://www.imwa.info/docs/Heavy_Metals_A_meaningless_term.pdf

There are some reasonably high flow options that can be used in conjunction with absorptive style reagents but the project contaminate levels and flow rates will determine the feasible options. Please don't hesitate to contact with more info. We may be able to help you sort out the best method to propose. 

Avoiding traditional methods of alkaline addition would be best as they are not stable long term. Sea Water neutralised bauxite refinery residues can be used to great effect if combined with appropriate process to catalyse the reagents...

You analyse water sample or solid sample ?

There are several publications going back more than 30 years that describe the use of gravel-based subsurface flow (SSF) constructed wetlands for heavy metals removal.  Unlike phytoremediation, the wetland plants do not take up the metals.  The sulfate reducing bacteria (SRB) at the bottom of the wetland slowly release a steady amount of hydrogen sulfide gas into the water column.  As this gas works it way to the surface, any divalent metal ions it encounters (e.g. Pb, Cu, Cd, Zn) it then forms an insoluble metal sulfide that accumulates on the bottom of the plastic-lined wetland.  A SSF wetland could be constructed with large gravel and/or strong plastic cages at the bottom of the plastic-lined wetland where the heavy metal sludge can accumulate.  On an annual or bi-annual basis, the sludge could be suctioned off and if desired, you could go through a metals recovery process.  To accelerate the initial development of the SRBs you can add gypsum (calcium sulfate) pellets to the gravel during the construction of the wetland.  Any other contaminants in the groundwater (nitrates, phosphates, organics, etc.) can also be removed by a combination of plant and bacterial processes.  This is a low-cost and low maintenance system.  

Stephen is entirely correct. 

It is a very slow remediation method though. 

see www.gardguide.com for more options - 

chapter 7 is useful. http://www.gardguide.com/index.php?title=Chapter_7

How much contamination do you have?

Dear Michael David Dickson,

It's about 500 mg/l

What time frame do you have - the total flow, the retention available, other physical constraints of the location and source?

residence time is about 4 hours, about 1 mg/min.

Your residence time is insufficient for bioremediation techniques. 

You will need to look at physio/chemical methods. 

What volume are we talking in those 4 hours?

 Michael has a valid point about the slow nature of biological metal uptake or sequestration.  Calcium Bentonite/Montmorillonite has one of the highest cation exchange capacities (CEC) of all known natural clays and it is quite inexpensive.  If you took your effluent and fed it into a decay gradient flocculation system and added a continuous solution of calcium bentonite and a flocculating agent such as poly-acrylic acid (PAA) you could remove all the metals in the desired time. When the clay is in suspension, the divalent heavy metals will displace the calcium in the clay matrix.  The  PAA or some next generation flocculating agent will bring the particles together and they will rapidly precipitate to the bottom of a settling tank.  I worked on a demonstration system like this more than 30 years ago and we treated about 400,000 L/day. The sludge can be collected, mixed with more clay and wastewater sludge to make pellets.  These pellets can then be fired in a rotary kiln to make construction grade light weight aggregate.  The metals are permanently bound within the ceramic matrix of the pellet and do not leach out even in a dilute acid digest.

 https://www.researchgate.net/profile/Malcolm_Clark

Is worth a look. Malcolm's work on the neutralised bauxite residues is very good. The reagents produces are extremely good candidates for use in the OCRA process.