Susmita; You should first ...

Susmita;

You should first get information describing the WW flow rate  and composition.  Without a characterization of the WW treatment need its impossible to provide a recommendation for an optimal treatment scheme.  Any proposals made without a LOT more information are simply attempts to get your business, they are not credible.   Some general information you’ll need to start determining what treatment steps are required include:

1. Anticipated flow rate & daily variability?  What are the concentrations of the typical WW contaminants and what heavy metals, radioactive, and biologically refractory organics are present in the WW and what are their anticipated mass loadings in the discharge?  A good WW characterization is the starting point for any WW treatment design.   Be careful to identify any instances where there could be significant changes in either flow or composition - these need to be accommodated in the design with either additional treatment capacity or with equalization capacity.   It’s also important to determine if there will be any increases in WW treatment requirements in the future - I have never known of a treatment system that didn’t eventually need to be expanded.   If you provide a treatment system, there are always others who will want to add their WW to it or the original need will increase for a variety of reasons.  Under-design is a very common problem.   Be careful of estimates of WW flow or composition that were made to reduce the cost of the system - this is a very common mistake that is costly to correct.  And it’s always prudent to design the system to allow expansion without major obstacles. 

2. Will this WW discharge be combined with any other WW streams prior to your treatment system?  Will there be any diluting WW mixed with it prior to treatment?  Will the discharge environment be part of the treatment or be used for dilution?  Understand what is meant by this.

3. Would it be possible to segregate any of the hospital’s individual streams prior to treatment - it’s always best to treat difficult contaminants in the most contaminated streams possible.   Treatment systems for some of the individual constituents are complex and expensive - dilution is not the solution.  If you can treat for them in a small stream, it will be lower cost and much more efficient.  This is especially important for contaminants not easily treated in conventional STP’s - heavy metals, radioactive constituents, refractory organics, etc.; all of which are likely concerns with a hospital WW stream.  You need to be especially careful with any contaminants that can bio-accumulate or ones that need to be removed to very low concentrations.  If the hospital can segregate these streams, it’s likely that they could be treated more efficiently as individual streams rather than as part of the entire WW stream - I stress the importance of this.
 

4.  To expand on the above... It’s likely that many of the more dangerous of these wastes will be relatively small volume waste streams and could likely be segregated without much effort.  In some cases they may simply be collected in specialized collection containers at the point of use & discharge.  Many will come from laboratories that typically collect solvents and other regulated wastes in separate containers (at least in countries with strict environmental regulations).  Dumping into the hospital drain/sewer is easy for the hospital employees but this can cause the treatment of the entire WW stream to be very complex and expensive - if handled responsibly.  I would hope the hospital would be supportive of efforts to allow their WW to be properly treated with minimal risk to people and the environment.  If the dangerous and difficult waste streams can be collected separately, they can be disposed of with technologies that wouldn’t be economically feasible for the entire WW discharge from the hospital.   
 
5. Be careful of any vendor suggestions for simple systems that don’t remove the dangerous contaminants and use dilution to coverup their presence.   The metals and any contaminants that can’t be biologically broken down to non-harmful elemental constituents need to be physically removed from the WW stream prior to discharge.  If they aren’t, they will accumulate in the area around the discharge - regardless of the volume of water providing the dilution.  Conservation of mass is a reality.  There are many systems that simply hide the contaminants either with dilution or by combining them with materials that make analytical detection very difficult.  These type of systems will eventually result in high concentrations of refractory organics and heavy metals in the food chain.  This typically takes years to become evident in the receiving environment.   But when it does, it can mean illness, loss of life and very, very expensive remediation efforts.  This is likely the most important design consideration - if you want an environmentally responsible design.  And be especially careful of accepting advice from any organizations selling systems which do not understand (or care) that their systems allow bio-accumulation.  Never put human life at risk to save money nor accept advice from people who place more importance on a sale than the consequences of what will happen. 

6. How sensitive is the receiving body - could the contaminants damage the area around the discharge?   Will the discharge provide nutrients that could result in algae blooms or could they upset the environmental balance in the discharge area? 

7. What are the environmental regulations in the area of the discharge?   The discharge should comply with all governmental requirements.  And it should also not represent a danger that isn’t properly regulated by the government.  The treatment should be responsible even if that means exceeding government requirements. 
 

The above is a quick list of things to consider.   It is by no means complete but it should hopefully get you going in the right direction.  Get with a design group that understands the needs and will design a system to meet the needs.   It’s unlikely that any individual vendor’s system will provide all of the treatment needs - don’t try a square peg for a round hole.  Vendors will always promise anything needed to get the contract.    Remember conservation of mass when evaluating whether a proposal will remove all of the contaminants in this WW.  I suspect that you will be presented with proposed systems that don’t accommodate this reality and it can be one of your first criteria for eliminating proposals.  
 

Good luck..