Can water treatment plants remove microplastics? What NJ systems do — and don’t — filter out

Published by NJ Clean Stream  |  Microplastics in NJ Drinking Water Series, Article 3 of 3

Treatment helps, sometimes substantially — but the degree of removal depends heavily on the treatment technology in use, the size and type of microplastics being targeted, and the critical gap between what conventional treatment achieves and what would be needed to eliminate meaningful human exposure. The particles that are most potentially harmful are the ones that are hardest to remove.

Conventional drinking water treatment: what it removes and what it doesn’t

Most of New Jersey’s larger surface water treatment plants use coagulation and flocculation, sedimentation, filtration through granular media, and disinfection. This conventional treatment train was designed primarily to address turbidity, pathogens, and chemical contaminants. Its performance against microplastics varies significantly by particle type and size.

Coagulation and flocculation causes fine particles and colloids to aggregate into larger floc particles. By incorporating microplastics into floc, it can remove 50 to 80 percent of microplastics from source water, depending on particle type and coagulant conditions.

Sedimentation removes particles dense enough to settle under gravity. Most microplastic particles are less dense than water — polyethylene and polypropylene float. Microplastics incorporated into denser floc can be removed; free-floating particles will not settle.

Granular media filtration through sand, anthracite coal, or other media provides physical straining and contact filtration. Studies have found that filtration brings overall removal to 70 to 95 percent in systems using conventional treatment. Filtration efficiency depends on particle size and shape: larger, irregularly shaped particles are captured more effectively than small, smooth particles or thin fibers.

The overall picture: Conventional surface water treatment removes a substantial fraction of microplastics — perhaps 70 to 95 percent — but leaves a residual that, given source water concentrations, can still represent tens to thousands of particles per liter in finished drinking water. For larger microplastic particles (greater than 100 micrometers), conventional treatment performs reasonably well. For smaller particles — and particularly for nanoplastics — it is far less effective.

Groundwater systems: a different picture

A significant fraction of New Jersey’s public water supplies — particularly in South Jersey — are drawn from groundwater. The microplastic exposure through groundwater-derived drinking water is generally lower than through surface water for two reasons: natural soil filtration removes particles larger than a few micrometers during infiltration, and deep, confined aquifers have no direct surface water input.

However, groundwater is not microplastic-free. Studies have detected microplastics in groundwater samples from various aquifer types. Nanoplastics — too small to be filtered by soil pores — can potentially reach groundwater directly. Fracture flow in bedrock aquifers can allow direct transport of small particles from the surface. For private well users in New Jersey, microplastic exposure risk from drinking water is generally lower than for surface water utility customers but is not zero, particularly for users of shallow wells in sandy aquifer systems.

The nanoplastics problem: what no current treatment removes

The most significant gap in drinking water treatment performance against microplastics — and the most concerning from a health standpoint — is the near-complete failure of conventional treatment to remove nanoplastics: plastic particles smaller than one micrometer.

Nanoplastics behave more like dissolved molecules than like particles in the hydraulic conditions of a conventional treatment plant. They pass through filter media that efficiently captures larger particles. They move through the treatment plant nearly as efficiently as the water itself.

The critical challenge: The health significance of nanoplastics is potentially greatest because of their small size — they can be absorbed across the intestinal epithelium, cross the blood-brain barrier, and enter cells through endocytotic uptake pathways. The studies detecting microplastics in human brain tissue, carotid artery plaque, and placental tissue are detecting particles in the nanoplastic and small microplastic size range — precisely the particles that current drinking water treatment is least effective at removing.

Advanced treatment technologies with higher microplastic removal

Membrane filtration — ultrafiltration and nanofiltration

Membrane processes use semi-permeable membranes with very small pore sizes to physically exclude particles. Ultrafiltration membranes (0.01 to 0.1 micrometer pore size) can physically exclude most microplastic particles, including smaller fractions that conventional treatment misses. Studies have found greater than 99 percent microplastic removal with ultrafiltration. Nanofiltration membranes have even smaller pore sizes and can exclude many nanoplastic particles.

Limitation: Significantly more expensive to install and operate than conventional filtration. Require careful pretreatment to prevent fouling. Generate a concentrated reject stream requiring management and disposal. Capital and operating cost premium for large water treatment plants can be tens of millions of dollars.

Reverse osmosis

RO achieves essentially complete removal of microplastics including nanoplastics. Its limitations are significant — it removes beneficial minerals, requires high operating pressure (high energy), and generates a large volume of reject water (15 to 25 percent of feed water). Appropriate for specific applications (desalination, arsenic removal, PFAS removal) but extremely expensive as a general approach to microplastic removal across New Jersey’s diverse water systems.

Enhanced coagulation

Optimizing the coagulation process — higher coagulant doses, adjusted pH designed to maximize microplastic capture — can improve conventional filtration performance without major capital investment. An incremental improvement that does not require large capital expenditure but still falls short of membrane filtration performance for smaller particle fractions.

What NJ Clean Stream is asking for

A three-phase regulatory response

  • Phase 1 — Mandatory monitoring: NJ DEP should require all community water systems serving more than 10,000 people to conduct annual microplastic monitoring of source water and finished drinking water, using standardized analytical protocols. Results reported to the NJ DEP and publicly disclosed in annual water quality reports. This characterizes the actual scope of NJ’s microplastic exposure and creates public accountability.
  • Phase 2 — Treatment performance assessment: Based on monitoring results, utilities with above-median microplastic concentrations in finished water should conduct a treatment performance assessment — evaluating what treatment optimization options are available, what advanced treatment technologies could reduce microplastic levels, and what the costs and benefits would be.
  • Phase 3 — Treatment improvement requirements: For utilities with significant microplastic concentrations and identified feasible improvements, the NJ DEP should establish treatment improvement schedules — phased over a reasonable period — requiring demonstrated microplastic reduction measures. Priority for utilities serving the most vulnerable populations and those with the highest source water concentrations.
  • Parallel track — source control: Washing machine fiber filter requirements, bottle bill expansion, tire rubber stormwater management, agricultural plastic reduction programs, and advanced tertiary treatment at major wastewater treatment plants. Source control and treatment optimization are complementary; neither alone is sufficient.

What residents can do while regulation catches up

Use a reverse osmosis filter. A point-of-use RO system installed under the kitchen sink will effectively remove microplastics — including the nanoplastic fraction that conventional treatment does not remove well — from the water used for drinking and cooking. RO systems also remove PFAS, arsenic, nitrate, and other contaminants. Regular maintenance and membrane replacement are required.

Avoid single-use plastic water bottles. Bottled water has been found to contain higher microplastic concentrations than tap water in some studies, likely because the bottling, shipping, and handling process introduces plastic particles from the packaging.

Wash synthetic textiles less frequently and at lower temperatures. Lower-temperature washing and shorter wash cycles reduce fiber shedding. A washing machine fiber filter can capture a significant fraction of shed fibers.

Engage in advocacy. Contact your water utility and ask whether it has conducted microplastic monitoring. Contact the NJ DEP and ask when it will require utilities to monitor for microplastics. Contact your state legislators and ask whether they support mandatory microplastic monitoring requirements.

This is Article 3 of 3 in NJ Clean Stream’s Microplastics in NJ Drinking Water Series. Article 1 introduces microplastics, their health implications, and the regulatory gap. Article 2 examines the sources of NJ’s microplastics and which are most controllable.