Your title refers only to ...

Your title refers only to odour removal. If this is the main issue then the simplest solution is to aerate the pond. The odours are generally caused when the pond goes septic.

Are the algae really a problem too? If so, covering the pond will prevent light entering and allowing green algae to grow, though you might get non-photosynthetic things growing instead. Alternatively use a chemical disinfectant (chlorine, sodium hypochlorite, or similar) if the chemical residual in the water doesn't create a problem for water re-use. This will also help to prevent odour by eliminating the bacteria which cause it to turn septic, and the chemicals are oxidising agents too.

Attempting to control the algae by improving the performance of the STP is unlikely to be effective because algae only require trace concentrations of nutrients to grow; you might slow them down but you're unlikely to prevent growth altogether.