Anaerobic Sludge Activity Test

Anaerobic sludge activity test – standard procedure -

WATERLEAU

Rev. 00

Date 22-12-2005

Status Draft

By W.L.

Checked BLM

Approved BLM

WATERLEAU nv – Radioweg 18 – 3020 Herent - Belgium Tel.: +32(0)16 650 657 - Fax: +32(0)16 650 663 -Email : info@ waterleau.com www.waterleau.com - BTW BE 438 047 842 – RPR Leuven KBC 432-0026651-22 – FORTIS 230-0049600-53 – BBL 335-0530911-76

Introduction In order to control the activity (good quality) of the sludge present in the diverse anaerobic wastewater treatment plants, a standard test is needed. The usually monitored parameters like COD removal, VFA levels (Volatile Fatty Acids), quantity and composition of biogas produced etc., do not reflect the composition of biomass under varied operational/environmental conditions.

Apparatus • • • • • • • • •

Balance, accurate to 0.01 g Oven or incubator, water bath or room set at 35 °C ± 0.5 °C pH meter Magnetic stirrer, with magnetic stirring bar Gas wash bottle, capacity 500 ml, fitted with a gas wash bottle head Graduated measuring cylinder, with a capacity of 2000 ml or more Nitrogen (N2) gas supply Erlenmeyer flask, 1000 ml, with a ground glass stopper Appropriate other glassware

Figure 1: Gas collection apparatus

Preparation of samples ƒ ƒ

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If the used sludge is not fresh, acclimatization and limited feeding of the sludge during several days is recommended to reactivate the sludge. Put an amount of sludge in the 1l Erlenmeyer to become a solution with TSS between 10 and 15 g/l. Fill up the Erlenmeyer with tap water. Stopper the Erlenmeyer and store for 24 hours at 35 °C Add 10 g of NaAc. 3aq; this is equivalent to ± 4.5 g COD Dissolve by magnetic stirring and bring to pH 7 with concentrated HCl or 10 % NaOH solution.

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Procedure ƒ

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Stopper Erlenmeyer with an appropriate open stopcock adapter with straight connection, preferably after flushing the head space with nitrogen (N2) gas. Put Erlenmeyer with sample on magnetic stirrer in a room or oven set at 35 °C. Connect the Erlenmeyer with the other glassware as follows (see also Figure 1): Attach the Erlenmeyer to the inlet of a gas wash bottle, containing 400 ml of 10% NaOH solution. Use appropriate silicone rubber tubing for connection of all glassware. Stir as gently as possible to keep the sludge in suspension. Let the produced gas bubble through the 10% NaOH solution, to absorb CO2. Methane gas is not absorbed. Collect the gas in a graduated measuring cylinder of 2000 ml or more, which is placed upside down in a container with acidified tap water (acidified till pH 2.0 with concentrated HCl or H2SO4), as follows: Fill the measuring cylinder to the brim with acidified water (pH 2.0), then invert into the container with acidified water (pH 2.0), so that the measuring cylinder is still full. Record the methane gas production at regular intervals by measuring the water displacement in the measuring cylinder. Run this test for 48 hours and put the results in a graph, as indicated in Figure 2.

Figure 2: Methane gas production

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Expression of results ƒ ƒ

Express the maximum gas production rate during phase 3 (see Figure 2)as: litre CH4 gas / (litre of sludge x day) If desired, measure the gas temperature in the cylinder (°C) and the atmospheric pressure (bar) and convert CH4 gas volume to normal volume (i.e. gas volume at 0 °C and 1.013 bar) with the following formula:

p 273 ⋅ atm 273 + T 1.013

Normal Volume CH 4 (l ) = Measured Volume (l ) ⋅ where: T = temperature (° C) patm = atmospheric pressure (bar)

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Normal litre CH4 gas / (litre of sludge x day) Since the production of 0.350 Nl (i.e. normal litre) CH4 gas corresponds to 1.0 g of COD removed, express sludge activity (by multiplying with 1/0.350) as: g COD removed / (litre of sludge x day) Measure the sludge concentration (both TSS and VSS) and express the results per g of VSS sludge or per g of TSS sludge: g COD removed / (g VSS x day) or g COD removed / (g TSS x day)

Interpretation of the results ƒ

Digested municipal sludge 0 – 0.05 g COD removed / (g of VSS x day) 0.05 – 0.10 0.1 – 0.2 > 0.2

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very poor sludge poor sludge average sludge good sludge

Methanogenic sludge from Methane Upflow Reactor 0.5 g COD removed / (g of VSS · day) 0.5 – 1.0 > 1.0

Anaerobic sludge activity test / Standard procedure

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poor sludge average sludge good sludge

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