WHY ATAD IS BETTER THAN AEROBIC DIGESTION

WHY ATADS ARE BETTER THAN AEROBIC DIGESTION

I have been accused of being excessively enthusiastic about ATAD. I have designed 2 facilities, Three Rivers, Michigan and Bowling Green, Ohio. The clients like them very much. I will distill down and demonstrate the reasons whey you should have an ATAD and try not to be too boring.

First, what is an ATAD (If I’m not being too pedantic)

Autothermal, meaning it generates its own heat

Thermophilic, meaning the reactor temperature is above 110 F, actually its about 150 F

Aerobic, meaning that during some of its operating cycle. It has a positive oxidation-reduction potential (ORP) and the end produce always does.

Digestion

ATAD is a two stage process. The first stage is a thermophilic stage, of about10-14 days. Autoheating conditions are produced by using a volumetrically efficient jet aeration system with a covered and insulated tank. Solids are fed daily and discharged daily.

The second stage, call a storage, nitrificatioin/denitrification reactor (SNDR) is a mesophilic stage. The digested biosolids have been pasteurized and have been stabilized, but it has a high polymer dose for dewatering. The high polymer dose is caused by biopolymers, which can be ndirectly measured as soluble COD (SCOD), and by monovalent ions (+1). The solids are cooled and aerated for 6-10 days to reduce the ammonia and SCOD, and produce an additional 10% TS reduction. Aeration is controlled to produce a nitrification/denitrification cycle and is controlled by pH or ORP. Solids are discharged daily and discharged daily or intermittently.

Digested ATAD biosolids can be stored as a liquid or dewatered. I suppose they could be dewatered on a sand drying bed as well. Liquid biosolids can be decanted in storage, but it takes several months to develop a supernating biota.

I could go on to a long article here, but I will summarize the ATAD advantages in this table.

PARAMETER	ATAD	AEROBIC DIGESTER
SRT	20 (with SNDR)	45
AERATION POWER	90 HP/DRY TON SOLIDS/DAY	130 HP/DRY TON SOLIDS/DAY
VS REDUCTION	55-75%	25-35%
TS REDUCTION	45-65%	20-30%
DEWATERED CAKE SOLIDS	BELT PRESS 22-24% CENTRIFUGE 30-40%	BELT PRESS 15-20% CENTRIFUGE 22-25%
EXCEPTIONAL QUALITY BIOSOLID?	YES	NO

Every installation, I believe, has seen a big reduction in biosolids beneficial reuse costs. Some success stories of which I know are

Bowling Green Ohio – Went from using 5 operators 65 days a year to haul bioslids to running a centrifuge and giving it away to a topsoil blender. Savings? About $200,000/yr.

Delphos OH - Went from paying $0.09/gallon to Mike’s Sanitation for taking their non class B sludge to giving it all away.

Marshall MN – Reduced liquid volume hauled by 65%

I will add some more later.

An ATAD makes sense at any installation with a capacity of 1 dry ton per day