Since you don't want to use coagulants/flocculants, the best  approaches are an automatic pressure filter (like an Oberlin, Pneumapress, or a Verti-press depending on the flow rate which again is stated; and the most important variable).

The second option would be a diaphragm filter press with a cloth washer. Both of these are batch, but there are many ways that a batch operation can be converted to a continuous operation.

The third option might be a decanter since you would be happy with 500mg/l in the effluent, (and this option would be continuous).

All of these are fairly costly, but testing will be required to get sizing as well as performance. The fact that you have anaerobically digested sludge suggests a difficult filtering material, (plus of course, the <50um particle size).