A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1990

Filamentous bulking is one of the problems in wastewater treatment that hinders the activated sludge to produce high quality of eff1uent and thus creating a threat to our environment. Such phenomenon is due to proliferation of certain types of filamentous bacteria which are enhanced by certain set of conditions. To cure this problem is to identify the filamentous bacteria that cause bulking and to know the condition s t h at has caused their excessive growth. Th is will give us a n idea on how to control them and inhibit their growth . Substrate composition a nd feeding pat tern are two major factors that affect their proliferation and they are dealt with in this research . Twelve experiments were undertaken in t his study. In every experiment, a combination of one carbon source - either glucose or acetic acid - a nd one nitrogen source - (NH4 ) 2S04 , NaN0 3 or peptone, together with other nutrients was used. Each kind of substrate composition was subjected to two feeding patterns , namely Continuously Stirred (Fed ) Tank Reactor (CSTR) system and Sequential Batch Reactor ( SBR ) system. Sphaerotilus natans has excessively grown in all substrate composition and has caused filamentous bulking in CSTR system. It h as appeared in all experiments (both CSTR a nd SBR ) with NaN03 as the nitrogen source and has caused bulking more rapidly in acetic acid than in glucose . Haliscomenobacter hydrossis has appeared in a l l experiments with (NH4 ) 2 S04 as nitrogen source. I t grew more in SBR system where growth of Sphaerotilus natans was suppressed and it was almost absent in CSTR sytem. Haliscomenobacter h ydrossis did not grow in acetic acid except only when nitrogen source was ( NH4 ) 2 S011. Haliscomenobacter hydrossis grew most in glucose-peptone medium than in any other substrate composition regardless of the feeding pattern. Its growth was better than Sphaerotilus natansin this medium. I n CSTR system, excessive proliferation of filamentous bacteria was observed. Al t ho ugh Haliscomenobacter hydrossis was moderate in n umbers and slowly growing , there was no filamentous bulking in SBR systems. Sphaerotilus natans was also slowly growing in glucose - NaN03 and glucose - peptone medium in SBR system. Th ese two types of filaments were t h e most common filament in t h e activated sludge that were investigated from t h e three wastewater treatment p l ants in Thailand . In addition Type 1702, Noscodia limicola, Type 1701 a nd Type II