The performance of the trickling filter/solids contact (TF/SC) process at high organic loadings was studied at the Morro Bay-Cayucos treatment plant. The average secondary effluent TSS increased only slightly (from 13 mg/L to 15 mg/L) when the filter BOD5 loading• was doubled from 480 g/m3 •day (30 ppd/ I 000 cu ft) to 960 gjm3 •days (60 ppd/ I 000 cu ft). The rock trickling filter operated without noticeableodors at the higher loading, although Beggiatoa presence indicated the filter was stressed. When the Morro Bay-Cayucos secondary process operated in the trickling filter mode at the lower filter loading, average secondary effluent TSS was 28 mg/L. Work at the Coeur d’Alene, Idaho, trickling filter plant showed that average secondary effluent TSS decreasedfrom 25 mg/L to 16 mg/L when the old shallow secondary clarifier wasreplaced with a new flocculator-clarifier. J. Water PoilU/. Contro/60, 68 (1988).