Sample sludge
Sludge sampling serves as a critical diagnostic for verifying the final quality of the treatment process. This protocol mandates the use of sanctioned container specifications, specific preservation methods, and strict maximum holding times to maintain the data integrity of the analysis. Central to this process is the accurate mapping of sludge disposal pathways, which dictates the required testing parameters. By ensuring that samples are truly representative of the facility's waste streams, suppliers can reliably demonstrate conformance.
Sludge disposal pathway
Wastewater treatment systems consist of many different processes resulting in many kinds of sludge. The following provides a comprehensive list and characteristics of different types of sludges, defining which are in-scope or out of scope for the applicability of the Wastewater and Sludge Guidelines. Common sludges and wastes generated at manufacturing facilities that are out of the scope of the guidelines are also included in this section.
In-scope
| Type of Sludge | Processes that Generate this Type of Sludge | Additional Process Information | Sludge Characteristics |
|---|---|---|---|
| Anaerobically digested secondary sludge | • Anaerobic contact reactor (ACR) • Anaerobic sequencing batch reactor (ASBR) • Up-flow anaerobic sludge blanket (UASB) etc |
This is a secondary (biological) treatment process involving microorganisms in the absence of oxygen. The digestion step takes place in a sludge digester and is a process used to reduce the organic loading and volume of the sludge. | Dark brown to black in colour and can contain an exceptionally large quantity of gas. When thoroughly digested, they are not offensive, the odour being relatively faint and like that of hot tar, burnt rubber or sealing wax. |
| Aerobically Digested Secondary Sludge | • Aerated lagoons, oxidation ponds, or aeration basins. | Sludge generated via secondary (biological) treatment processes involves microorganisms in the presence of oxygen. Digestion steps take place in a sludge digester and are used to reduce organic load and volume of sludge. | Brown to dark brown and have a flocculent appearance. Odour is not offensive; it is often characterised as musty. Well-digested aerobic sludge dewaters easily. |
| Primary Treatment Sludge | • Primary settling tank or primary clarifier • Consists of coagulation, flocculation, sedimentation and clarification processes. • This treatment step frequently involves the addition of chemicals to aid in coagulation and flocculation, including inorganic chemicals and organic polymers. |
Substantial quantities of gas may be given off and the sludge density increased by long residence times in storage. | Sludge from primary settling tanks is usually grey and slimy and, in most cases, has an extremely offensive odour. • Sludge from chemical precipitation with metal salts is usually dark in colour, though its surface may be red if it contains much iron. • Lime sludge is greyish-brown. • While chemical sludge is somewhat slimy, the hydrate of iron or aluminium in it makes it gelatinous. |
| Biomass or Secondary/Tertiary Treatment Sludge | • Rotating biological contactors (RBCs) • Membrane bio reactors (MBRs) • Moving bed biofilm reactor (MBBR) • Submerged aerated filter (SAF) • Activated sludge processes and secondary clarifiers • Processes which involve microorganism or bacteria in presence of oxygen • Trickling filters Tertiary treatment processes including: • Chemical precipitation and separation in a clarifier • Fenton process • Ozonation • Reverse osmosis • Nanofiltration • Ultrafiltration • Microfiltration |
Secondary / tertiary treatment may be used to remove organic compounds, nitrogen, phosphorus, additional suspended solids, heavy metals, and dissolved solids. | Generally has a brown flocculent appearance. Tertiary sludge may be light brown in colour and less odorous. • If the colour is dark, the sludge may be approaching a septic condition. • If the colour is lighter than usual, the sludge may have been under aeration with a tendency for the solids to settle slowly. • Sludge in good condition has an inoffensive "earthy odour". • When sludge contains many worms, it may become inoffensive quickly. Trickling-filter sludge digests readily. |
| Mechanically dewatered sludge "cake" | • Floatation • Gravity belt filter press • Thickening drum • Screw drum • Centrifuge • Plate and frame press |
Sludge dewatering is the separation of solid and liquid phase in order to create a solid called sludge "cake". | Dewatered sludge cake contains moisture in the range of 65% - 85%. This type of sludge may be brown and have an offensive odour. |
| Dried sludge or ash | • Sludge drying beds • Sludge dryer • Mechanical evaporation • Thermal drying • Thermal evaporator • Ash from onsite incineration |
Sludge drying is the process of further reducing moisture content of sludge in order to reduce volume and transportation costs. On-site incineration of sludge (with or without energy recovery) is considered to be a treatment step, and the ash must be collected and disposed of properly. |
Sludge drying processes are used to produce sludge with water content of less than 10 to 20 weight percent moisture. |
| Adsorption or filtration system waste | • Various filtration processes using media like sand, activated carbon, resins, and similar materials. | Media used to remove organic compounds (including MRSL compounds) or media used to remove metals in wastewater must be changed out periodically. | Appearance can vary depending on the media being used. |
Out of scope
| Type of Waste | Description of the Type of Waste | Processes that Generate this Type of Waste |
|---|---|---|
| Screening waste | Includes all types of organic and inorganic materials large enough to be removed by large mechanical screens (bar racks), lint screens, or other screens. The organic content varies, depending on the nature of the system. | Generated by mechanical pretreatment process (mechanical screening). Screening is done manually or automatically using screens with different mesh sizes. |
| Grit waste | Usually made up of the heavier inorganic solids (including sand) that settle with relatively high velocities. Depending on the operating conditions, grit may also contain significant amounts of organic matter, especially fats and grease. | Generated by hydro-mechanical process. |
| Scum/grease waste | Consists of the floatable materials skimmed from the surface of primary and secondary settling tanks and from grit chambers and chlorine contact tanks, if so equipped. Scum may contain grease, vegetable and mineral oils, animal fats, waxes, soaps, paper, plastic materials, grit particles, and similar materials. | Scum is collected by skimming processes. Grease may come from machinery or from kitchen/cafeteria areas and may also be removed by skimming processes. |
| Chemical cleaning waste | Machine cleaning chemicals are used for cleaning knitting or weaving machines, dyeing machines, sewing machines, etc. Floor cleaning chemicals are used for cleaning floors. | Any waste generated due to cleaning of chemical containers and drums. |
| Print paste waste | Waste generated from print paste residues, screen making, screen cleaning or other activities related to printing. | May be generated in the manufacturing facility or in a separate area. |
| Other waste not specifically listed in the "in scope" section | All other waste generated in the manufacturing facility or the wastewater treatment system that is not comingled with In Scope sludge is considered to be out of scope. | Refer to the list of In Scope wastes above. Comingling means the mixing of wastes together prior to disposal. |
Sludge disposal means the final placement or incorporation of sludge (and ash from the incineration of sludge) into a permanent storage location or state, such that the sludge poses no or very low risk to human health and the environment. Disposal also includes the incorporation of sludge and ash into building products, or in the case of sludge going to land application, the safe and beneficial incorporation of sludge into an acceptable land area.
- Pathway A - Off-site incineration at >1000 °C
- Pathway B - Landfill with Significant Control Measures
- Pathway C - Building Products Processed at >1000 °C
- Pathway D - Landfill with Limited Control Measures
- Pathway E - Off-site Incineration and Building Products Processed at <1000 °C
- Pathway F - Landfills with No Control Measures
- Pathway G - Land Application
Sludge sample collection
The suppliers must identify to qualified sampling personnel the locations where sludge is generated and stored at the supplier facility. The qualified sampling personnel will determine the proper sampling locations as per the guidance provided to them.
Collected sludge samples must be representative of the chosen ZDHC Disposal Pathways.
- Precipitation/flocculation/coagulation to remove organics
- Anaerobically digested secondary treated sludge
- Aerobically digested secondary treated sludge
- Primary treated sludge
- Biomass, secondary treated and tertiary treated sludge
- Mechanically dewatered sludge
- Dried sludge.. Sludge generated from evaporation processes
- Ash from the incineration of any type of waste at an on-site incinerator
- Samples shall only be taken by trained and qualified samplers. Laboratories can nominate samplers to train using the Solution Provider Platform.
- Composite sludge samples are one sludge type taken over a period of time. The composite sludge sample can be taken from a hopper, roll-off or sludge storage areas. It must represent the facility’s sludge production and storage cycle for the entire volume of that sludge type.
- At facilities with on-site incineration, the sampler will collect and separately test two samples:
- Residual incineration ash
- Composite sludge
- Sludge samples should be collected as composite samples following the USEPA 833-B- 89- 100. 1 The ISO 5667- 13 “Guidance on Sampling Sludge” document also provides reference sludge sampling guidance and more detailed information on sampling devices. The most appropriate way of sampling in any situation depends on several factors:
- Safe access to the sampling point by personnel.
- The practicality of installing and maintaining automatic equipment (if appropriate).
- To produce a sample from multiple sample locations (e.g. two or more de-watering units), combine the grab samples from each location (equal amounts or weighted, based on flow or solids flux data) in a plastic or stainless-steel bucket and thoroughly mix the sample (with a scoop or spoon). Then transfer it to sample containers.
- When sampling drying beds, divide each bed into quarters. From the centre of each quarter, collect a single core sample through the entire depth of the sludge using a coring device. Usually, a small amount of sand will be collected. Avoid large amounts of sand. Combine and thoroughly mix in a plastic or stainless-steel bucket and transfer to sample containers.
- A sample shall be collected as one composite sample of that sludge type. The composite sample shall represent the entire volume of that sludge type. A sampling grid pattern may be needed, and core samples may be required to obtain a representative sample. Collect samples in a manner that represents the entire sludge volume.
In general, automatic sampling devices, which are widely used for wastewater streams, do not work well for sludge streams because of the solids content and viscosity of sludges. Due to this, manual composite sampling is required.
- For collecting solid and semi-solid sludge samples:
- When sampling heaps of air-dried sludge lifted from drying beds or stockpiles of sludge cake, it is important to obtain portions of sludge from throughout the mass; not just from the surface layer.
- For de-watered cakes, dried sludge powder or compost products, combine equal amounts collected at various locations/depths for each grab sample. This will obtain a more representative composite sample.
- To produce a sample from multiple sample locations (e.g. two or more de-watering units), combine the grab samples from each location (equal amounts or weighted, based on flow or solids flux data) in a plastic or stainless-steel bucket and thoroughly mix the sample (with a scoop or spoon). Then transfer it to sample containers.
- When sampling drying beds, divide each bed into quarters. From the centre of each quarter, collect a single core sample through the entire depth of the sludge using a coring device. Usually, a small amount of sand will be collected. Avoid large amounts of sand. Combine and thoroughly mix in a plastic or stainless-steel bucket and transfer to sample containers.
- A sample shall be collected as one composite sample of that sludge type. The composite sample shall represent the entire volume of that sludge type. A sampling grid pattern may be needed, and core samples may be required to obtain a representative sample. Collect samples in a manner that represents the entire sludge volume.
- All laboratory sample containers must be filled from the same bulk composite sample. A minimum sample volume of six (6) litres is needed to fill all the containers. The laboratory may require extra volume for quality assurance samples.
- Collect samples in a manner that represents the entire flow at the sampling point, over the entire sampling period.
- These procedures should be followed when sampling from a tap:
- Allow sufficient time following pump start-up to clear the line of stagnant sludge.
- Allow sludge to flow from the tap for several seconds prior to sampling. This will flush out stagnant sludge and solids accumulated in the tap.
- To prevent solids separation in the sample, use glass stirring rods or stainless-steel spoons to mix the sample before splitting or transferring any portion of it to another container.
- With sludge processing trains, samples from taps on the discharge side of sludge pumps are well mixed since flow at this point in the system is turbulent with minimal solids separation within the flow stream.
- If a sample is drawn from a tap on a pipe containing sludge that is distant from the sludge pumps, the average flow velocity through the pipe should be greater than 2 feet per second (fps). Average velocities of less than 2 fps (0.6 m/s) result in solids separation and settling and affect sample solids content, depending on the location of the tap (top, side or bottom of the pipe).
- Given a choice, a tap on the side of the pipe is preferable. In addition, the tap should be a large size to encourage draw from the entire cross-section of flow when fully open without clogging the flow.
- If the sludge solids tend to separate into different fractions, mix the samples adequately to obtain a representative sample. If they do not mix, collect separate samples. Some pollutant parameters are predominantly associated with the solid fraction, while others are associated with the liquid phase.
Sampling equipment must be made of materials that will not contaminate or react with the sludge and must have adequate capacity to avoid oxidation if the bottle is not completely filled. The best material choices are glass and stainless steel because they are relatively inert.
If available, sludge flux (weight/time) and/or sludge flow data (volume/time) must be collected and reported with the laboratory test report. Typically, the sludge dewatering equipment is not operated 24/7 and will run 2 or 3 cycles per day, depending on equipment sizing and sludge volume produced. Monitoring flow rates will not represent the daily operations and flows/generation of sludge. In such cases, sludge flux and flow data are not necessary to collect or record.
The facility shall provide all necessary assistance to the sampler, including but not limited to:
- Access to all relevant areas.
- Provision of information, e.g. flow rates, facility layout, flow path processes, etc.
- Relocation of parts of solid sludge piles where needed to access deeper layers.
- Provision of safety gear and warnings on any specific hazards present.
Note : The declaration will be collected by samplers during the sludge sample collection and submitted to their lab.
Download sludge disposal pathway declaration template
Sludge sample containers and preservatives
Solution providers should:
These can vary depending on the analytical procedure used. Therefore, verify the proper container and preservative with the analytical method used at the laboratory.
Caution should be exercised as containers can become pressurised due to gas production in wastewater sludges and explosive situations can occur. Care should be taken, particularly when glass containers are used, to prevent a build-up of gas pressure and to minimise the dispersion of fragments if an explosion occurs.
A temperature indicator bottle shall be included with each shipping container to measure the temperature of samples at their time of arrival at the laboratory. The temperature indicator bottle will be clearly labelled.
When collecting samples, fill the container to 4/5 full to enable expansion of samples and provide room for gases that may be produced.
For solid sludge samples (cake, powder, ash), adding a chemical preservative is generally not useful since the preservative does not usually penetrate the sludge matrix. Preservation is achieved by keeping the temperature between 2°C and 8°C.
The table below presents the recommended containers for each sludge parameters
Sludge Sample Containers and Preservatives Table
Sludge Sample Containers and Preservatives for MMCF Facilities Table
Sludge sample holding time
The table below presents the recommended and maximum holding times for each of the sludge testing parameters.