A HORIZONS FEATURE

City Dust

Road Markings

* Marine Coatings 3.7%   Personal Care Products 2%   Plastic Pellets 0.3%

FIBER

MICROPLASTICSSmall plastics that are produced, such as nurdles and microbeads (primary), or those that degrade from larger pieces of plastic (secondary). Scientists have found microplastics in a dizzying array of places, from human blood and stool to sea ice in the Arctic.

DERIVATION

FILM

Primary

Secondary

NURDLES

MICROBEADS

COMMON SOURCESThese are the four most common sources* of microplastics in our environment. Synthetic textiles and vehicle tires account for more than half of the world’s volume of microplastic debris. Common sources of ingestion of microplastics by the public include:     • Tap Water     • Bottled Water     • Seafood     • Select Crops     • Clothing Microfibers     • Beer, Plastic Tea Bags

Synthetic Textiles

FOAM

Vehicle Tires

Although most plastic water bottles can be easily recycled, only 15-35% end up in recycling facilities.  

80%

End up in landfills

10-2

It can take up to 1,000 years for plastic water bottles in landfills to fully decompose.

10-3

10-4

10-5

10-6

1 mm

10-7

1 cm

10-8

1 nanometer

10-9

VIRUS

1 micrometer

DNA (2 nm)

SIZE-BASED CLASSIFICATION The regulatory definition of microplastics includes nanoplastics.

VISIBLE TO NAKED EYE

Macro- plastics

Small (1-100 µm)

DEFINITION

TOXICITY Microplastics can adsorb orders of magnitude more chemicals than the water around them. Microplastics may include three separate vectors including: inherent toxicity of the insoluble particle, adsorbed chemicals, and microbial pathogens as biofilms.

>2.5 cm

15%

SMALL HEX NUT (5 mm)

35%

100- 1000 nm

Meso- plastics

Recycled Plastic Water Bottles

Sub-Micron Plastics

5-25 mm

BOTTLED WATER One plastic bottle will, over time, break down into more than 10,000 micro-plastic pieces. Bottled water consistently has higher amounts of microplastics than tap water.

SHAPES along 3 axes 

1 nm-100 nm

Three TypesPOLYMETRICComposition of >=1% polymeric materials by mass.  SYNTHETICDoes not occur naturally in the environment.  SOLIDSMaterials cannot be considered a liquid or a gas.

MICROPLASTICS (MP)

Nanoplastics (NP)

Large (100- 5000 µm)

BIOSOLIDS APPLICATION When conducting mass balances on wastewater treatment plants, a noteworthy percentage of microplastics are often not traced after the influent. It is believed that these microplastics could occur in the sludge. REDUCED YIELD Accumulation of microplastics in soil from biosolids has been linked to decreased agricultural yield

BIOSOLIDS APPLICATION

HOME

DISTRIBUTION

SYNTHETIC FIBERS Shed from garments in washing machines and drain with the effluent water at much higher volumes than personal care products and cosmetics. More than 1,900 microplastic fibers can be released from a single synthetic garment in one wash cycle. These fibers can pass through the most commonly used screen filters in wastewater treatment facilities.

COMMUNITY

Microplastics Pathways

INFLUENT WATER SYSTEM

BIOMAGNIFICATION

FISHING INDUSTRY

Deep Well Injection

Water Cycle

RAINWATER

Surface Runoff/Leaching

WATER RESOURCE RECOVERY FACILITY (WRRF)

Incinerator

WRF Treated Effluent

Landfill

WRF Residuals

WRRF Treated Effluent

GROUND WATER

Treated Effluent

WATER TREATMENT PLANT (WTP)

SURFACE WATER

Intake

Combined Influent

FINISHED DRINKING WATER

WATER RESOURCE FACILITY (WRF)

WTP Residuals

OCEAN WATER

PATHWAYS Microplastics in drinking water, wastewater effluent, stormwater, and biosolids are a rising challenge across the globe. A myriad of sources for microplastics enter wastewater facilities, typically hindering utilities from decreasing their occurrence. Beyond municipal sources for microplastics, industrial, stormwater, landfill, and food waste slurry may increase concentrations in the effluent and/or biosolids.

WASTEWATER Combined influent from wastewater collection systems collect microplastic debris from the environment and other sources. Microplastics that meet current reporting criteria often constitute a vast majority of those identified in wastewater effluent. Removal rates dramatically vary by facility type and the processes employed.

WATER TREATMENT Coagulation, flocculation, and sedimentation in drinking water treatment plants remove high percentages of large and small microplastics. Advanced treatment further increases removal rates. Finished drinking water typically contains relatively low concentrations of large and small microplastics. Widespread quantification of submicron plastics and nanoplastics in drinking water has not yet been established.  

BIOSOLIDS Residuals from wastewater treatment processes are often further conditioned along solid stream processes then land-applied through beneficial reuse as biosolids. Microplastics in biosolids may accumulate in the soil and early studies indicate plant uptake may occur. Microplastics from the biosolids may also be removed from the upper portions of amended soil to occur in agricultural runoff 

BIOSOLIDS

WRRF

WRF

DISPLACEMENT

OCEAN WATER Studies indicate that the ultimate fate of many microplastics is in deep sea sediment. 

WATER CYCLEMillions of tons of minute plastic debris travel by air, land, and sea, transported in our planet’s water cycle. Precipitation, runoff, and infiltration deposit the pollutants. Evaporation, transpiration, and condensation, return debris to the atmosphere.

BIOMAGNIFICATION Biomagnification of micro- plastics is occurring, beginning with the smallest organization in the food chain – zooplankton. FISHING INDUSTRY Residue from nets, fishing line, and paint fragments from boat hulls, contribute to microplastic debris.  

WTP

DESIGNED AND PRODUCED BY HAZEN AND SAWYER • COPYRIGHT © 2023

i

CAYLA COOK, PE Cayla is a technical expert on specific soluble and particulate contaminants in water and wastewater. 

Lower Removal Rates

DISPOSAL

REMOVAL RATESResearch is still in the earliest stages for determining the removal rate of various technologies for microplastics. Not all studies quantify removal rates for all particle size ranges, therefore, studies on the same technology may lead to different results when quantifying dramatically different size ranges. Some treatment types or aged infrastructure may, in fact, increase microplastic levels.

Higher Removal Rates

REVERSE OSMOSISPerhaps the most puzzling of all results are a variety of removal rates for reverse osmosis (RO). Studies have indicated that zeta potential and temperature play a strong role in the removal of micropollutants that may be associated with microplastics. The size range and morphology, e.g., fibers and fragments, may play a strong role in their removal efficiency. * Sand filtration data is incomplete due in part to the many variations of sand filtration types/designs.

OXIDATIONStudies often indicate an increase in microplastic quantities following oxidation. This could be due to the embrittlement of softer plastic types like microfibers and/or breakdown caused by shear force. This is also a topic of research in recent years to determine if this degradation can be harnessed for beneficial purposes.

MBRsWhile MBRs are indicated for a higher removal rate than some other technologies, challenges arise with impacts to reversible and slight irreversible membrane fouling due to microplastics. NOTE: A wide range of different materials, additives, and degrees of weathering, e.g., fragility of the environ- mental particles, provide greater difficulty in comparing laboratory studies to actual influent microplastic qualities.