Reducing the Amount of Waste Activated Sludge

Sara Schmidt

CE 479

December 6, 2006

Overview of Presentation:

Background information Concerns regarding waste activated

sludge What is MicroSludge®? Design comparisons of two digester

systems

Background Information

Primary sludge – produced from the primary settling of untreated wastewater

Waste activated sludge (WAS) – excess sludge produced from activated sludge process

CMAD – Conventional Mesophilic Anaerobic Digester

Mesophilic – operating temperature of 25 - 40°C

Background Information

Thermophilic – operating temperature of 50-60°C

MicroSludge – Sludge pre-treatment that greatly enhances the performance of digesters

Concerns Regarding WAS:

Risks to public health from sludge residuals

High capital and operating costs

Contribute to the public’s growing concerns regarding odors

Negative environmental impacts

How much waste do people really produce?

A typical secondary wastewater treatment plant that serves 1 million people generates 25 football fields (about three feet deep) of biosolids each year.

What is MicroSludge®?

MicroSludge works by destroying microbial cell membranes and enabling anaerobic digesters to achieve significantly greater conversion of WAS to biogas.

www.microsludge.com

MicroSludge and Microbes

The image to the left shows intact microbes (magnified 20,000 times)

The image to the right shows the same microbes after the MicroSludge process

Benefits of MicroSludge

Major reduction in WAS residual biosolids (VSr)

Lowers retention time => additional digester capacity

Increased amount of biogas production

Reduces operating, disposal, & mixing costs

MicroSludge Location in a Wastewater Treatment Plant

Design Parameters (Design 1)

Q = 2Mgal/d = 7440 m3/d Dry volatile solids = 0.16 kg/m3

Biodegradable COD removed = 0.17 kg/m3 HRT (hydraulic retention time) = 15 days Efficiency of waste utilization, E = overall

VSr = Mass fractionPS x VSrPS + Mass fractionTWAS x VSrTWAS = (0.65 x 0.68) + (0.35 x 0.45) = 0.60 = E

Design Parameters

Y = 0.08kg VSS/kg bCOD utilized Kd = 0.03d-1

Digester gas is 65% methane Sludge contains 94% moisture, 6% solids

= 0.06 = Ps

Sludge has a specific gravity, Ssl = 1.02

Calculations

Sludge volume

= [Ms] ÷ [(Ssl)(ρw)(Ps)]

= [(0.16 kg/m3)(7440 m3/d)] ÷

[1.02(103 kg/m3)(0.06)]

= 19.45 m3/d

Calculations

bCOD loading

= (0.17 kg/m3)(7440 m3/d)

= 1265 kg/d

HRT = V/Q => V = Q * HRT

= (19.45 m3/d)(15 d)

V1 = 292 m3

Calculations

bCOD in inffluent, So

So = 1265 kg/d

bCOD in effluent, S

S = 1265(1 - E)

= 1265(1 – 0.60) = 506 kg/d

Calculations

Quantity of volatile solids produced per day, Px

Px= [Y(So – S)] ÷ [1 + (kd)(HRT)]

= [0.08kg VSS/kg bCOD(759)] ÷

[1 + (0.03d-1)(15 d)]

Px(1) = 41.88 kg/d

Calculations

Volume of methane produced per day @ 35°C, VCH4

VCH4 = (0.40)[(So – S) – 1.42Px]

= (0.40m3/kg)[759 kg/d –

1.42*(41.88 kg/d)]

VCH4 = 280 m3/d

Estimate total gas production

= 280/0.65 = 430 m3/d

Design Parameters (Design 2)

Q = 2Mgal/d = 7440 m3/d Dry volatile solids = 0.16 kg/m3

Biodegradable COD removed = 0.17 kg/m3 HRT (hydraulic retention time) = 15 days Efficiency of waste utilization, E = overall

VSr = Mass fractionPS x VSrPS + Mass fractionTWAS x VSrTWAS = (0.65 x 0.68) + (0.35 x 0.97) = 0.78 = E

Design Parameters

Y = 0.08kg VSS/kg bCOD utilized Kd = 0.03d-1

Digester gas is 65% methane Sludge contains 94% moisture, 6% solids

= 0.06 = Ps

Sludge has a specific gravity, Ssl = 1.02

Calculations

Sludge volume

= [Ms] ÷ [(Ssl)(ρw)(Ps)]

= [(0.16 kg/m3)(7440 m3/d)] ÷

[1.02(103 kg/m3)(0.06)]

= 19.45 m3/d

Calculations

bCOD loading

= (0.17 kg/m3)(7440 m3/d)

= 1265 kg/d

HRT = V/Q => V = Q * HRT

= (19.45 m3/d)(13 d)

V2 = 253 m3

Calculations

bCOD in inffluent, So

So = 1265 kg/d

bCOD in effluent, S

S = 1265(1 - E)

= 1265(1 – 0.78) = 278 kg/d

Calculations

Quantity of volatile solids produced per day, Px

Px= [Y(So – S)] ÷ [1 + (kd)(HRT)]

= [0.08kg VSS/kg bCOD(987)] ÷

[1 + (0.03d-1)(13 d)]

Px(2) = 56.79 kg/d

Calculations

Volume of methane produced per day @ 35°C, VCH4

VCH4 = (0.40)[(So – S) – 1.42Px]

= (0.40m3/kg)[987 kg/d –

1.42*(56.79 kg/d)]

VCH4 = 362 m3/d

Estimate total gas production

= 362/0.65 = 557 m3/d

Comparison of two designs

Without using MicroSludge (Design 1):– V(1) = 292 m3

– Px(1) = 41.88 kg/d

– VCH4 = 280 m3/d

With using MicroSludge (Design 2):– V(2) = 253 m3

– Px(2) = 56.79 kg/d

– VCH4 = 362 m3/d

Cost Comparison

The major difference between these two designs are the volume needed for the digesters, volatile solids production, and methane gas production .

These differences are a major cost reductions for a wastewater treatment plant.

Questions???