Definitely high-rate anaerobic digestion (HRAD) after equalization, pre-acidification and conditioning. Up to 95% of the COD can be converted to methane (green energy).
We designed and realized many such HRAD units. If interested, I would be happy to mail you more.
There are many ways to treat it, and the best way will depend on the influent and effluent standards as the resource you have.
If you have enough area you can think in lagoons or aerated lagoons, if you have small area, then you can think in direct filtration (various steps). In many cases the equalization or homogenization tanks could be necessary. Other times you could need special skilled operators when you have a high technology plant. Of course each technology has its own purchase and/or construction costs and its own operation cost that can lead the Total Cost of Ownership, and may times the TOC will lead the purchase decision if you evaluate the project at some rears looking for the best Return Of Investment (ROI).
At this time we are quoting an MBBR (2 steps) to treat 200 m3/d and COD = 8000 ppm with just 25,2 m2 in footprint for the MBBR and other 12,6 for the settling tank using our special media
I recommend you consider of the simplest system you can find, is the biocleaner bioreactor that can be submerged and continually produce microorganisms in the aerated basin to digest even part of the organic sludge. This system could be used in actual WWTP to upgrate or in a new design.
EEC www.eecusa.com a leader in MBBR since 1984 with Global Production and Services since 1984 - Send us the influent and effluent req. and we can quote.