Material Recovery Facility Contamination Audit and Diversion Improvement Project

This project prepares a material recovery facility contamination audit and diversion improvement package. The objective is not to report a high recycling number. The objective is to prove how much material is actually recovered, how much is rejected downstream, which equipment or incoming streams create contamination, and what engineering controls improve verified diversion.

A material recovery facility, or MRF, behaves like a production system with uncertain feedstock. Incoming material varies by route, season, user behavior, moisture, particle size, packaging, and prohibited items. The facility must sort useful products, reject residuals, protect workers, prevent fires, maintain equipment reliability, and document where the material goes.

The central project question is:

Which changes will improve verified material recovery without hiding contamination, residual disposal, safety risk, or downstream rejection?

The answer must close a mass balance and connect process data to buyer acceptance.

Project Objective

Prepare an audit and improvement plan for a single-stream recycling MRF. The final deliverable must include:

1. boundary definition and stream map;
2. inbound waste characterization;
3. mass balance across product, residue, storage, and unmeasured loss;
4. reported diversion versus accepted recovery;
5. contamination and buyer-rejection analysis;
6. sorting capacity and bottleneck check;
7. safety and reliability risk review;
8. improvement actions with validation evidence;
9. final decision on whether the facility can claim improved diversion.

The project is written for environmental engineering students and early-career engineers. It uses simplified values, but the workflow is the same as a real audit: the facility must reconcile scale tickets, samples, residues, rejected bales, stored inventory, maintenance downtime, contamination sources, buyer feedback, and environmental controls.

Baseline Scenario

A regional MRF receives mixed recyclables from municipal routes and commercial accounts. The facility has a tipping floor, presort station, screens, magnets, eddy-current separator, optical sorters, manual quality-control stations, balers, product storage, and residue transfer compactors.

Management reports that the facility diverts more than 40\% of incoming material. Buyer complaints suggest that some shipped bales are too contaminated, and residue loads are rising. The engineering team is asked to perform a contamination audit and propose improvements.

Item	Value
average inbound mass	150\ \text{t/day}
audit period	10\ \text{operating days}
nominal operating time	8\ \text{h/day}
shipped recovered products	64\ \text{t/day}
buyer-rejected recovered products	10.5\ \text{t/day}
residue sent to disposal	72\ \text{t/day}
product storage increase	4\ \text{t/day}
estimated moisture and fines loss	unknown at start
optical sorter nominal capacity	18\ \text{t/h}
target accepted recovery rate	at least 40\% of inbound mass
maximum allowed buyer rejection	5\% of shipped recovered products

The audit must distinguish:

• material shipped from the MRF;
• material accepted by buyers after quality checks;
• material rejected or downgraded by buyers;
• residue sent to disposal;
• storage changes;
• unmeasured loss such as moisture, fines, dust, scale error, or reporting mismatch.

Deliverable Structure

The audit package should include:

Section	Engineering evidence
boundary and stream map	scales, storage points, rework loops, residue transfer, buyer returns
sampling plan	route samples, product-bale samples, residue audits, sample mass, time basis
mass balance	inbound mass, products, rejects, residues, storage, unexplained difference
contamination diagnosis	contaminant type, source route, process location, buyer impact
capacity check	feed rate, equipment capacity, downtime, bottleneck and bypass behavior
safety review	batteries, pressurized cylinders, sharps, fires, dust, traffic and lockout risk
improvement plan	source controls, presort, screen cleaning, optical sorter settings, QC staffing
validation plan	accepted recovery, buyer reject rate, residue composition, downtime and incidents

The deliverable should be auditable. A later dispute about diversion or product quality should be traceable to scale records, sample records, bale IDs, buyer feedback, and operating logs.

Step 1: Close the Facility Mass Balance

The facility receives:

It ships:

It sends residue to disposal:

Product storage increases:

The unmeasured balance term is:

Substitute:

Engineering Comment

The 10\ \text{t/day} difference is 6.7\% of inbound mass:

That may represent moisture loss, fines, dust, stockpile measurement error, bypass, scale mismatch, or incomplete records. The project should not accept a diversion claim until this difference is explained or bounded.

Step 2: Reported Diversion Versus Accepted Recovery

Reported shipment diversion is:

Substitute:

However, buyers reject:

Accepted recovered mass is:

Accepted recovery is:

Engineering Comment

The facility appears to exceed a 40\% diversion target if only shipped mass is counted. It fails the target when buyer rejects are removed. This is the core audit finding: diversion is not verified until downstream acceptance is included.

An engineering report should avoid vague language such as “recovered material was shipped.” It should state whether material was accepted, downgraded, reworked, landfilled, stockpiled, or returned.

Step 3: Buyer Rejection Rate

Buyer rejection as a fraction of shipped recovered products is:

Substitute:

The maximum allowed buyer rejection is 5\%, so the exceedance is:

Engineering Comment

A 16.4\% rejection rate is not a small bookkeeping issue. It means the facility is transferring contamination downstream. It also makes diversion claims fragile because some material counted as product will eventually become residue elsewhere.

The audit should identify which product streams drive the rejection. A mixed paper bale with film plastic and food residue requires different corrective action from a PET bale contaminated by PVC or a metal bale contaminated by aerosol cans.

Step 4: Residue Composition Audit

A residue audit estimates the recoverable material still leaving in residue.

Category in residue	Fraction of residue	Mass in residue
recoverable cardboard and paper	9\%	6.48\ \text{t/day}
recoverable rigid plastics	6\%	4.32\ \text{t/day}
recoverable metals	2\%	1.44\ \text{t/day}
glass fines not marketable	11\%	7.92\ \text{t/day}
true residuals and contamination	72\%	51.84\ \text{t/day}

The recoverable mass currently lost to residue is:

If half of that recoverable mass can be captured and accepted by buyers, added accepted recovery is:

Revised accepted recovery would be:

Revised accepted recovery rate:

Engineering Comment

Capturing half of the recoverable material lost to residue almost reaches the 40\% accepted recovery target, but not quite. The improvement plan must also reduce buyer rejection or inbound contamination. The residue audit shows opportunity, but it does not by itself prove target compliance.

Step 5: Sorting Capacity Check

The facility processes:

over:

Average feed rate is:

The optical sorter nominal capacity is:

Capacity ratio:

Engineering Comment

The optical sorter is being loaded at about 104\% of nominal capacity before downtime, surges, wet material, and maintenance are considered. This can explain increased contamination and recoverable material in residue.

An improvement that only tells operators to “pick better” will not solve an overloaded separation step. The feed rate, presort burden, screen condition, and product-quality station must match the real flow.

Step 6: Capacity Improvement Screen

The team proposes two changes:

1. remove film plastic and bulky nonconforming items at presort before they reach screens;
2. extend the processing window by 0.5\ \text{h/day} during the first validation month.

Presort improvement reduces effective optical-sorter feed by 9\%:

With a longer window:

Average line feed for the same inbound mass is:

If both effects apply, the effective sorter load is:

Capacity utilization becomes:

Engineering Comment

The sorter now has operating margin. The project should validate whether this margin reduces residue recoverables, buyer rejects, jams, and manual rework. A capacity calculation is only useful if it changes measured contamination and accepted recovery.

Step 7: Cost of Buyer Rejection

Buyer-rejected bales create direct and indirect cost. Use a simplified direct cost model:

Cost item	Value
lost product revenue	110\ \text{USD/t}
rehandling and rework	35\ \text{USD/t}
residual disposal after rejection	85\ \text{USD/t}

Cost per rejected tonne:

Daily rejection cost:

If the improvement reduces buyer rejection from 10.5 to 4.0\ \text{t/day}:

Daily avoided cost:

Engineering Comment

This calculation does not include contract penalties, lost buyer trust, overtime, vehicle trips, fire incidents, or public reporting risk. The actual value of contamination control is often larger than direct rejection cost.

The cost screen is useful because it connects environmental performance to facility operating discipline. Better recovery is not only a sustainability claim; it is product-quality control.

Step 8: Safety and Reliability Risk Review

Contamination is also a safety issue. The audit identifies batteries, pressurized cylinders, sharps, aerosol cans, and tangled film as high-risk items.

Failure mode	Effect	Initial S	Initial O	Initial D	Initial RPN
lithium-ion battery reaches paper line	fire in product stream	9	4	5	180
aerosol can enters baler	rupture or worker injury	8	3	5	120
tangled film overloads screen	downtime and bypass	5	6	4	120
glass fines contaminate paper bale	buyer rejection	4	6	4	96
unlabeled returned bale	traceability loss	6	3	5	90

The largest initial RPN is battery fire risk:

Controls include:

• inbound education and route feedback for battery contamination;
• presort battery watch with safe collection container;
• thermal monitoring at product storage;
• stop-work rule for smoking, heating, odor, or damaged batteries;
• bale quarantine and traceability for suspect loads.

After controls:

Controlled RPN:

Engineering Comment

Severity remains high because a fire can still harm workers, equipment, products, and air quality. The controls reduce occurrence and improve detection. A MRF improvement plan is incomplete if it improves recovery while increasing fire or worker-safety risk.

Step 9: Improvement Plan

The proposed project actions are:

Action	Expected effect	Validation evidence
route feedback for high-contamination sources	reduce prohibited items at inbound	route-level contamination samples
presort film and battery station	reduce screen wraps and fire risk	presort log, battery count, downtime record
screen cleaning interval	reduce glass and fines carryover	product-bale contamination samples
optical sorter feed-rate control	improve capture and product purity	throughput, sorter reject rate, residue audit
QC sampling at bale release	prevent low-quality shipments	bale sample records and buyer acceptance
returned-bale traceability	close loop on buyer complaints	bale ID, route, shift, operator, corrective action

The plan should run for one validation month. The audit should compare before and after values for:

• accepted recovery rate;
• buyer rejection rate;
• residue recoverable fraction;
• optical sorter load;
• screen downtime;
• battery and aerosol-can incidents;
• mass-balance closure.

Step 10: Readiness and Release Decision

Define a simple readiness score for the improvement package.

Item	Weight	Score
mass-balance basis approved	5	4
sampling plan approved	5	4
presort station staffed and trained	4	3
battery safety controls installed	5	5
optical sorter feed-rate control active	4	3
bale QC sampling active	4	4
buyer feedback loop active	4	3
residue audit repeated after changes	4	2
route feedback process active	3	2
traceability for returned bales active	3	3

Total possible:

Actual score:

Readiness index:

Engineering Comment

An 80.5\% readiness index supports a controlled trial, not permanent claims of improved diversion. The hard gates are:

1. battery safety controls must be active before changes increase manual presort exposure;
2. bale QC sampling must be active before products are shipped under the new process;
3. a repeated residue audit must confirm that recoverable material in residue actually decreases;
4. buyer rejection must fall below the agreed limit before public diversion claims are updated.

The correct decision is:

Proceed with a one-month controlled improvement trial. Do not claim improved diversion until accepted recovery and buyer rejection data close the loop.

Validation Targets

The improvement trial should pass these targets:

Metric	Baseline	Target
accepted recovery rate	35.7\%	at least 40.0\%
buyer rejection rate	16.4\%	below 5.0\%
optical sorter utilization	104\%	below 90\%
recoverable material in residue	12.24\ \text{t/day}	below 7.0\ \text{t/day}
unexplained mass-balance term	10\ \text{t/day}	below 5\ \text{t/day} or explained
battery fire-risk RPN	180	below 60 with active controls

If all targets pass, the facility can report the improved accepted recovery rate with supporting records. If shipped mass improves but buyer rejection remains high, the change is not successful.

Final Deliverable

The final project file should include:

• facility boundary and process-flow map;
• inbound scale records and sampling basis;
• daily mass balance with storage and unexplained terms;
• reported diversion and accepted recovery calculations;
• product-bale contamination data and buyer rejection records;
• residue composition audit with recoverable material estimate;
• feed-rate and sorter-capacity calculations;
• cost of buyer rejection and avoided-cost screen;
• safety and reliability FMEA for high-risk contaminants;
• improvement plan with owners, validation targets and hard gates;
• release decision for trial, normal operation, or hold.

Common Mistakes

• Reporting shipped material as recovered material without confirming buyer acceptance.
• Ignoring storage changes and unexplained mass-balance differences.
• Blaming public behavior without checking equipment overload, screen condition, sampling quality and buyer specifications.
• Improving diversion percentage by transferring contamination to another facility.
• Treating residue as uniform waste without auditing recoverable material still present in it.
• Running higher throughput through an already overloaded sorter.
• Focusing only on recycling rate while ignoring batteries, fires, worker exposure, air emissions, odor and residual disposal.
• Announcing improved diversion before enough post-change data exist.

Transferable Lesson

Resource recovery is an environmental engineering and quality-engineering problem. The useful metric is not how much material leaves the facility in a bale. The useful metric is how much material is accepted downstream, how much residual remains, what contamination was controlled, and what evidence proves the result.

A credible MRF improvement project closes the mass balance, measures contamination, checks capacity, controls safety risks, follows returned material back to its source, and validates the claim with accepted recovery rather than optimistic shipment totals.