Tertiary Treatment of Wastewater: Phosphorus Removal, Constructed Wetlands & Polishing
What the chemistry actually requires — lime, luxury uptake, alum at 200–400 mg/L, and an unusually honest field assessment of constructed wetlands. Built on the New Mexico Wastewater Systems Operator Certification Study Manual, Chapter 12.
▶ Watch: Tertiary Wastewater Treatment: Advanced Polishing for Phosphorus & Nitrogen Removal
Processes designed to remove pollutants OTHER than the common BOD and TSS.
That is the whole boundary. Secondary handles BOD and solids; tertiary handles what is left.
Source: NMED / NMSU WUTAP Operator Certification Study Manual, January 2005 · Verify against current practice
About the Source
| Item | Detail |
|---|---|
| Document | New Mexico Wastewater Systems Operator Certification Study Manual |
| Prepared by | Water Utilities Technical Assistance Program (NMSU DABCC WUTAP) |
| For | Facility Operations Section, NMED Surface Water Quality Bureau, Santa Fe |
| Date | January 2005 |
| Length | 238 pages, 16 chapters |
| Tertiary content | Chapter 12 (Tertiary Treatment) and Chapter 13 (Nitrogen Removal), plus tertiary ponds in Chapter 5 |
This manual dates to 2005. The chemistry, the process principles and the operator guidance are durable — lime still precipitates phosphorus the same way, and luxury uptake works on the same biology.
What may have moved: regulatory limits, New Mexico Water Quality Commission standards, and the state of practice on membrane filtration and newer biological nutrient removal configurations.
This guide reproduces the manual faithfully and flags where the field has developed since. VERIFY CURRENT PERMIT LIMITS AND STATE STANDARDS SEPARATELY.
Part 1 — What Tertiary Treatment Is
The manual’s definition
Tertiary treatment is the name given to processes designed to remove various pollutants from the wastewater stream other than the common BOD and TSS.
— NM Operator Certification Study Manual, Chapter 12
That is a cleaner boundary than most textbook definitions. It is not about being third in sequence, and it is not about a particular technology. It is defined by TARGET — anything you are removing that is not carbonaceous oxygen demand or suspended solids.
The three subjects the manual covers
| Subject | Where | Note |
|---|---|---|
| PHOSPHORUS REMOVAL | Chapter 12 | Lime precipitation, luxury uptake, alum flocculation |
| NITRIFICATION AND DENITRIFICATION | Chapter 13 | Treated as its own chapter — nitrogen removal |
| CONSTRUCTED WETLANDS | Chapter 12 | Covered candidly — see Part 3 |
| Tertiary / polishing ponds | Chapter 5 | Organic loading of 5–15 lbs BOD5 per acre per day |
Not filtration. Not disinfection. NUTRIENTS — phosphorus and nitrogen.
That reflects why tertiary treatment exists in the first place: secondary treatment handles the oxygen demand and the solids, and what remains to threaten a receiving water is the nutrient load that drives algae.
Filtration appears in this manual as a SUPPORT PROCESS for phosphorus removal rather than as an end in itself — which is a useful way to think about it.
Where tertiary sits in the sequence
| Stage | Removes | Covered in the manual at |
|---|---|---|
| Pretreatment | Screenings, grit | Chapter 3 |
| Primary | Settleable solids | Chapter 6 |
| Secondary | BOD and suspended solids | Chapters 7, 8, 10 |
| TERTIARY | Everything else — principally nutrients | CHAPTER 12, 13 |
| Disinfection | Pathogens | Chapter 9 |
| Solids handling | The sludge from all of it | Chapter 11 |
Part 2 — Why Phosphorus
The mechanism of harm
Phosphorus combined with inorganic nitrogen poses serious pollution threats to receiving waters because of high algae growths which result from the presence of the two nutrients in water.
— Chapter 12
| Step | What happens |
|---|---|
| 1 | Phosphorus provides a nutrient or food source for algae. |
| 2 | Combined with inorganic nitrogen, it drives high algae growth in the receiving water. |
| 3 | Algae are considered unsightly and CAN CAUSE TASTES AND ODORS IN DRINKING WATER SUPPLIES. |
| 4 | DEAD AND DECAYING ALGAE CAUSE SERIOUS OXYGEN DEPLETION in receiving streams. |
| 5 | That oxygen depletion KILLS FISH AND OTHER AQUATIC WILDLIFE. |
The regulatory logic
The manual states it simply: by removing phosphorus from the effluent, the lake or river receiving the discharge has one less nutrient essential for algae growth, and that reduction limits algae growth. EPA and other water quality agencies recognize the need to protect rivers and lakes from excessive algae, and consequently require plants to remove phosphorus.
Algae need both nitrogen and phosphorus. Remove either one far enough and growth is constrained regardless of how much of the other is present.
Phosphorus is frequently the easier and cheaper of the two to remove chemically, which is why phosphorus limits appear in permits so often.
This is also why the manual pairs phosphorus removal and nitrogen removal as the two halves of tertiary treatment — they are the same problem attacked from two directions.
Part 3 — Constructed Wetlands: An Unusually Honest Assessment
Most published material on constructed wetlands is promotional. This manual is not — it walks through the theory, then documents where New Mexico systems failed to deliver it.
That makes it genuinely useful content. An operator or a designer reading only the promotional material is being set up for the exact problems catalogued here.
Everything in this part is the manual’s assessment, reproduced faithfully.
The theory
| Element | Detail |
|---|---|
| Purpose | Small-scale wastewater treatment, with the focus being nitrogen removal. |
| Biology | Operate much the same way as natural wetland processes. |
| Mechanism | Wetland plants take up the nutrients in the wastewater. |
| Expectation | To NITRIFY AND DENITRIFY using a combination of microbiological growth and aquatic plants. |
| Typical plants | Bulrushes and cattails. |
| Two forms | SUBSURFACE FLOW (reed beds) and OVERLAND / POND. |
| The difference | Whether the wastewater is allowed to surface and be acted on by sun and wind. |
Subsurface flow — how it is supposed to work
Wastewater is distributed through pipes below the surface in a bed of gravel or pumice. The manual notes it OPERATES MUCH LIKE A TRICKLING FILTER — a microbiological colony establishes on the media and removes nutrients. Units are often paired with septic tanks, which were meant to remove settleable solids that would otherwise clog the media. The bulrushes and cattails were also supposed to deliver oxygen to the subsurface, preventing septic conditions and odors.
What the manual says actually happens
| Problem | The manual’s account |
|---|---|
| NO LARGE-OBJECT REMOVAL | "Often found lacking in the design of the systems is an adequate method for removal of the large objects common to wastewater streams." |
| GRIT ACCUMULATION | Grit accumulation causes a LACK OF DETENTION TIME IN THE SEPTIC TANKS. |
| MEDIA PLUGGING | Unavoidable suspended solids from the septic tank, combined with THE INABILITY OF THE MEDIA TO SLOUGH OFF SOLIDS AS A TRICKLING FILTER DOES, plugs the media and forces wastewater to the surface anyway. |
| ODORS | High oxygen demand on the bed allows the water to turn septic in the septic tank. That high oxygen demand plus the suspended solids FORCE HIGH OXYGEN DEMAND WATER TO THE SURFACE WHERE ODORS DEVELOP. |
| NITROGEN REMOVAL | Citing W. Daniel Boivin, Evaluation of Constructed Wetlands Performance in New Mexico: SUBSURFACE FLOW CONSTRUCTED WETLANDS ARE INCAPABLE OF REMOVING THE NITROGEN IN SEPTIC TANK EFFLUENT TO THE NEW MEXICO WATER QUALITY COMMISSION STANDARDS. |
| THE ROOT CAUSE | "Key to this is the need for additional oxygen to assist in the nitrification process." |
The manual: "One of the big selling points in the constructed wetlands systems is the lack of maintenance needed in the system. IN ACTUAL OPERATION THIS HAS NOT BEEN THE CASE."
It adds that maintenance is ESSENTIAL for these systems to operate at even the minimal levels obtained in the field, and that annual removal of vegetative growth is needed to keep them healthy.
And the line worth quoting on any page about wetlands: THIS VEGETATIVE GROWTH IS THE SLUDGE REMOVED FROM THE SYSTEM.
Further: MOST OF THE SYSTEMS HAVE REQUIRED MECHANICAL AERATION, which comes with associated electrical and maintenance costs — undercutting the passive, low-energy premise entirely.
Overland flow wetlands
| Point | Detail |
|---|---|
| The advantage | Surface application PREVENTS THE PLUGGING OF THE MEDIA noted in subsurface flow. |
| Closer to nature | The environment more closely simulates a natural wetland. |
| Common design | Lagoon-type systems are commonly incorporated, providing additional oxygen and treatment through conventional algae and wind action. |
| ODORS REMAIN | "It stands to reason that a constructed swamp would produce the same type of swamp gasses that are produced in natural wetlands." |
| BOD loading | The design most often seen DOES NOT PROVIDE FOR THE BOD LOADING coming from a septic tank. |
| Debris | Care must be taken to remove accumulated debris. |
| Mosquitoes | Addition of GAMBUSIA (a mosquito-eating fish) may be warranted. |
Where wetlands do work
The most successful wetland operation has been at the end of conventional treatment processes such as Activated Sludge, or Lagoons. In this manner the wetland operates as a polishing process.
— Chapter 12
The manual finds wetlands succeed as a POLISHING STEP behind conventional secondary treatment — not as a treatment process in their own right behind a septic tank.
The filtering action of the media and plant growth is described as A VIABLE OPTION FOR THE FILTERING OF TSS AND NON-SOLUBLE BOD in treated effluents.
THE CATCH, stated immediately: "The problem with this is the filtering will also lead to clogging of the wetlands."
And on nitrogen: TREATMENT FOR REMOVAL OF NITROGEN HAS NOT BEEN AS SUCCESSFUL. Most reported data is described as SPORADIC AND INCONSISTENT, with long-term testing by Michael Richard, Ph.D. on Colorado systems showing PERIODIC PURGING OF NITROGEN AND PHOSPHORUS by the wetland systems.
A wetland that accumulates nutrients in plant biomass and then releases them in pulses is not removing nitrogen and phosphorus — it is storing and returning them on its own schedule.
That is precisely why the manual insists on annual vegetation removal. THE HARVEST IS THE REMOVAL STEP. Without it, the nutrients go back into the water.
If you take one operational point from this section, it is that.
Part 4 — Wetlands Operation and Maintenance
While there is very little an operator can do to control or improve the operation of wetlands, there is maintenance required.
— Chapter 12
The maintenance program
| Task | Detail |
|---|---|
| DIKES | Maintain them. Plant a LOW GROWING GRASS to prevent erosion; cut regularly and dispose of clippings. |
| BURROWING ANIMALS | Attracted by the lush vegetation. Discourage them from burrowing into the ground around the wetlands. |
| HOUSEKEEPING | Essential for odor, insect and rodent control. Screenings and grit from pretreatment removed DAILY and disposed of properly. No trash accumulation. |
| VEGETATION REMOVAL | At the end of the growing season. This is the removal step — see Part 3. |
| Mosquito control | Gambusia may be warranted on overland flow systems. |
Burning the vegetation — the manual’s procedure
The manual gives a specific, practical procedure that is easy to overlook and expensive to skip.
CARE NEEDS TO BE TAKEN TO PROTECT THE LINING OF THE WETLANDS as well as ANY EXPOSED PLASTIC PIPE — sampling ports and distribution pipes.
THE METHOD: cover exposed pipe with WET BURLAP, then enclose it with a 5-GALLON BUCKET before setting the wetland on fire.
PERMITS FOR BURNING must be obtained from the proper authorities.
And ensure A GOOD SUPPLY OF WATER AND MANPOWER is available to prevent the fire escaping the wetland area.
The alternative: cut the plants and remove and properly dispose of the cuttings.
Process control testing
| Test | Frequency | Target / note |
|---|---|---|
| Effluent DO | At least TWICE A WEEK | MAINTAIN A MINIMUM EFFLUENT DO OF 0.5 mg/L |
| Effluent pH | At least twice a week | — |
| Effluent temperature | At least twice a week | — |
| Total nitrogen | Weekly or at least monthly | SAMPLE BOTH INFLUENT AND EFFLUENT |
| Nitrate nitrogen | Weekly or at least monthly | Effluent |
| Flow | Continuous, with totalizer | MEASURED AT BOTH INFLUENT AND EFFLUENT of the facility |
The manual does not just list tests — it names the response: "BASED ON THIS TESTING, CHANGES TO THE FLOW PATTERN SHOULD BE MADE TO MAINTAIN A MINIMUM EFFLUENT DO OF 0.5 mg/L."
Flow pattern is essentially the only control handle an operator has on a wetland. That is what the earlier line about "very little an operator can do" means in practice.
The influent-and-effluent nitrogen sampling requirement connects directly to the percent removal logic in the influent vs effluent guide in this series.
Records
The manual is specific about what to keep: flow and process control testing records, A COPY OF THE AS-BUILT DRAWINGS, and all permit testing done on the facility. It adds that DAILY RECORDS OF TEMPERATURE AND WEATHER CONDITIONS will help in troubleshooting — which makes sense for a process driven by biology, sunlight and season.
Part 5 — Phosphorus Removal: Lime Precipitation
The chemistry
When lime — calcium hydroxide, Ca(OH)₂ — is mixed with plant effluent in sufficient concentration to bring about a high pH, a compound forms consisting of PHOSPHORUS, CALCIUM AND THE HYDROXYL ION. That compound can be flocculated into heavier solids that settle in a clarifier.
The manual notes that A SUBSTANTIAL AMOUNT OF THE LIME REACTS WITH THE ALKALINITY OF THE WASTEWATER to form a calcium carbonate precipitate, which settles out with the phosphorus sludge.
That is lime you paid for that is not removing phosphorus. It is consumed by the alkalinity, and it adds to your sludge volume.
It also means a high-alkalinity wastewater costs more lime per pound of phosphorus removed — and it produces more sludge to handle. Worth knowing before you budget either.
This is the same alkalinity that Part 6 of the alkalinity guide in this series treats as a resource to be protected for nitrification. Here it is a chemical demand to be paid for.
The three reactions
| Step | What happens |
|---|---|
| 1. COAGULATION | Chemical addition REDUCES THE ELECTROMAGNETIC FORCES that keep suspended particles apart. The electrical charge on the particles is altered so that suspended particles containing phosphorus TEND TO COME TOGETHER RATHER THAN REMAIN APART. |
| 2. FLOCCULATION | Occurs after coagulation. The collection or agglomeration of suspended material into LARGER PARTICLES. Gravity causes these larger particles to settle. |
| 3. SEDIMENTATION | The settling of heavy suspended solid material due to gravity. Solids settling to the clarifier bottom are removed by pumping and other collection mechanisms. |
They get used interchangeably in conversation and they are distinct operations with distinct equipment.
COAGULATION is chemical — neutralizing the charge that holds particles apart. It needs rapid, energetic mixing.
FLOCCULATION is physical — gently bringing the destabilized particles together into settleable floc. It needs SLOW mixing; too much energy tears the floc apart.
A plant with a flocculation basin mixing too fast is undoing the chemistry it just paid for.
Equipment required
| Component | Purpose |
|---|---|
| Lime feeding systems | Chemical delivery |
| Mixing and flocculation areas | The two-stage process above |
| Chemical clarifiers | Sedimentation |
| Pumps and piping | Removal of lime phosphorus sludge |
| pH ADJUSTMENT FACILITIES | For the effluent — lime raises pH substantially |
| Lime recovery | Listed by the manual as part of the equipment set |
| Sludge disposal facilities | The phosphorus sludge |
Lime precipitation works BY RAISING pH. The manual specifies that the process requires facilities for pH ADJUSTMENT OF THE EFFLUENT.
You cannot discharge water at the pH that made the chemistry work. Secondary treatment standards under 40 CFR 133.102 require effluent pH between 6.0 and 9.0, and receiving-water limits may be tighter.
That is a second chemical feed, a second cost, and a second thing to control. Any evaluation of lime precipitation that omits it is understating the system.
Part 6 — Phosphorus Removal: Luxury Uptake
The biology
Bacteria found in normal activated sludge process use phosphorus within the make-up of the cell structure that forms the bacteria.
— Chapter 12
| Condition | What the bacteria do |
|---|---|
| In a proper environment with food and oxygen | They ABSORB PHOSPHORUS QUITE FREELY — taking in excess phosphorus beyond their structural need. This is LUXURY UPTAKE. |
| Placed in an ANAEROBIC environment | Phosphorus is THE FIRST ELEMENT RELEASED as they begin to die. The manual describes them as FACED WITH THE SITUATION OF APPARENT DEATH. |
| At the release point | The released phosphorus can be drawn off and removed from the wastewater stream. |
| Returned to aeration | Lacking phosphorus in their cell structure, THE FIRST THING THEY TAKE IN IS PHOSPHORUS — and the cycle repeats. |
You are not removing phosphorus chemically. You are deliberately starving bacteria until they dump their phosphorus, harvesting it, then feeding them so they over-consume replacing it.
THE MANUAL’S OPERATIONAL WARNING: "The bacteria should not be allowed to die. However, the length of time should be sufficient to remove as much of the phosphorus as possible."
That is a narrow window, and the manual says the operator MUST CLOSELY REGULATE THE TIME OF THE ANAEROBIC CONDITION.
Too short and you release little phosphorus. Too long and you lose the biomass that does the work.
The physical arrangement
| Unit | Detail |
|---|---|
| Base plant | A standard activated sludge plant. |
| ANAEROBIC BASIN | A relatively DEEP DETENTION BASIN where anaerobic conditions exist. |
| LIME CLARIFICATION TANK | Usually capable of treating 10 PERCENT OF THE WASTEWATER FLOW STREAM through the facility. |
| Return pumps and piping | Move activated sludge through the anaerobic state to a phosphorus release point and back to aeration. |
| The cycle | Remove sludge from the secondary clarifier → anaerobic detention → release → return to aeration where sufficient oxygen and primary effluent exist so the bacteria REVIVE and take up maximum phosphorus. |
The lime clarification tank in a luxury uptake system handles only about a tenth of plant flow, because it is treating the concentrated release stream rather than the whole effluent.
That is the economic advantage over straight lime precipitation — you are dosing chemical into a small sidestream instead of the entire flow.
It is also a reminder from the sidestream discussion in the influent vs effluent guide: a small-volume, high-concentration return stream can carry a large share of a plant’s nutrient load.
The constraint
The manual is direct about the limitation: because luxury uptake can only take place in a very controlled environment, THE BACTERIA CANNOT BE EXPOSED TO ANY CONDITION WHICH WOULD PREVENT THEM FROM EITHER TAKING UP PHOSPHORUS INTO THEIR CELL STRUCTURE OR RELEASING THE PHOSPHORUS AT THE PROPER TIME. Anything that upsets the activated sludge process — toxicity, a load slug, a DO failure — upsets the phosphorus removal along with it.
Part 7 — Phosphorus Removal: Alum
The chemistry and the numbers
| Item | Detail |
|---|---|
| Chemical | Aluminum sulfate (alum) |
| First reaction | Alum reacts with THE ALKALINITY of the wastewater to form an ALUMINUM HYDROXIDE FLOC. |
| Removal mechanism | Formation of an INSOLUBLE COMPLEX PRECIPITATE, and by ADSORPTION ON THE ALUMINUM HYDROXIDE FLOC. |
| DOSAGE | 200 TO 400 mg/L of alum, depending on the alkalinity of the wastewater. |
| RESULT | Reduces effluent phosphorus to 0 TO 0.5 mg/L. |
| OPTIMUM pH | Usually achieved AROUND pH 6.0. |
| Dose control | Frequently controlled by AUTOMATIC pH EQUIPMENT dosing to a pH set point — THE MORE ALUM, THE LOWER THE pH. |
| Determining the setpoint | JAR TESTS can be used to determine the optimum pH set point and alum dosage rate. |
The manual states the alum dose range of 200–400 mg/L is DEPENDING ON THE ALKALINITY OF THE WASTEWATER.
So alkalinity does not just consume chemical as a side reaction; it is the variable that sets where in that two-fold range your dose lands.
A high-alkalinity wastewater sits at the top of the range. That is potentially double the chemical cost for the same phosphorus result — which makes influent alkalinity a number worth knowing before you specify an alum system.
The settling problem, and why a filter follows
"This alum floc is difficult to settle out in a clarifier. THEREFORE, A SAND OR MIXED-MEDIA FILTER IS USUALLY PLACED AFTER THE CLARIFIER to remove the remaining floc."
And again for low residuals: "If it is necessary to achieve low effluent phosphorus residuals (LESS THAN 1.0 mg/L), the chemical clarifier is usually followed by EITHER A PRESSURE FILTER OR A MULTI-MEDIA GRAVITY FILTER."
THIS IS WHERE TERTIARY FILTRATION ACTUALLY ENTERS THE PICTURE in this manual — not as a standalone process but as the step that catches what the chemistry could not settle.
Anyone specifying alum phosphorus removal to a tight limit is specifying a filter whether they planned to or not.
Lime versus alum
| Factor | LIME | ALUM |
|---|---|---|
| Chemistry | Ca(OH)₂ — raises pH | Aluminum sulfate — lowers pH |
| Optimum pH | High | Around 6.0 |
| Reacts with alkalinity | Yes — forms CaCO₃ precipitate | Yes — forms aluminum hydroxide floc |
| Settling | Settles in a clarifier | FLOC DIFFICULT TO SETTLE — filter usually needed |
| Effluent pH adjustment | REQUIRED | — |
| Chemical recovery | Lime recovery listed among the equipment | NO ECONOMICAL METHODS AVAILABLE FOR ALUM RECOVERY |
| COST | More commonly used | — |
| The manual’s verdict | "Because of the difference in cost between aluminum sulfate and lime, LIME IS MORE COMMONLY USED for the precipitation of phosphorus." | — |
LIME CAN BE RECOVERED — the manual lists recovery facilities as part of the lime precipitation equipment set. ALUM CANNOT: "At present, there are no economical methods available for alum recovery."
And phosphorus sludge from either process goes to dewatering and disposal. Both chemicals ADD SLUDGE VOLUME on top of what the plant already produces — lime through the calcium carbonate precipitate, alum through the hydroxide floc.
A chemical phosphorus removal decision is also a solids handling decision. Chapter 11 of the manual covers that side.
Part 8 — Tertiary and Polishing Ponds
Loading rates from Chapter 5
| Pond type | Organic loading (lbs BOD5 per acre per day) |
|---|---|
| Anaerobic | 200–1,000 — and greater than 14 feet deep |
| Facultative | 15–50 |
| TERTIARY / POLISHING | 5–15 |
Source: Chapter 5, Wastewater Treatment Ponds.
A polishing pond is not a different structure from a facultative pond. It is the same thing operated at roughly a third to a tenth of the organic load.
That low loading is what allows it to finish the job rather than do the job — and it is why the manual describes ponds in series after a trickling filter plant as GIVING A FORM OF TERTIARY TREATMENT.
The manual also notes that ponds in series CAN PROVIDE A HIGH QUALITY EFFLUENT WHICH IS ACCEPTABLE FOR DISCHARGE INTO MOST WATERCOURSES, and that IF THE DETENTION TIME IS LONG ENOUGH, MANY PONDS CAN MEET FECAL COLIFORM STANDARDS.
Part 9 — Operator Summary and Quick Reference
The decisions this chapter supports
| If you need to… | Consider |
|---|---|
| Remove phosphorus at lowest chemical cost | Lime precipitation — more commonly used on cost grounds, and recoverable. |
| Remove phosphorus biologically | Luxury uptake — no bulk chemical on the main stream, lime clarifier sized for ~10% of flow. |
| Hit a phosphorus limit below 1.0 mg/L | Chemical clarifier PLUS a pressure filter or multi-media gravity filter. |
| Reach 0–0.5 mg/L phosphorus | Alum at 200–400 mg/L, pH around 6.0, with filtration. |
| Polish TSS and non-soluble BOD | A wetland behind conventional secondary — accepting that it will clog over time. |
| Polish generally at low cost | Tertiary ponds at 5–15 lbs BOD5/acre/day. |
| Remove nitrogen | Chapter 13 — nitrification and denitrification. NOT wetlands, on this manual’s evidence. |
Quick reference
| Item | Value |
|---|---|
| Tertiary treatment, defined | Removal of pollutants OTHER than common BOD and TSS |
| Main subjects | Phosphorus removal; nitrification and denitrification; wetlands |
| Phosphorus removal types | Lime precipitation, luxury uptake, alum flocculation with filtration |
| Lime chemistry | Ca(OH)₂ + phosphorus + calcium + hydroxyl at high pH |
| Lime side reaction | Reacts with alkalinity → CaCO₃ precipitate in the sludge |
| Three reactions | Coagulation → flocculation → sedimentation |
| Lime requires | Effluent pH adjustment facilities |
| Luxury uptake — release | Anaerobic conditions; phosphorus is the FIRST element released |
| Luxury uptake — uptake | Return to oxygen and food; phosphorus taken up first |
| Luxury uptake — clarifier size | ~10% of plant flow |
| ALUM DOSE | 200–400 mg/L, depending on alkalinity |
| ALUM RESULT | 0–0.5 mg/L effluent phosphorus |
| ALUM OPTIMUM pH | ~6.0 |
| Alum dose control | Automatic pH equipment to a set point; jar tests to find it |
| Alum floc | Difficult to settle — sand or mixed-media filter after the clarifier |
| For P below 1.0 mg/L | Pressure filter or multi-media gravity filter after the clarifier |
| Alum recovery | None economical |
| Lime vs alum | Lime more commonly used on cost |
| Wetland effluent DO target | MINIMUM 0.5 mg/L — adjust flow pattern to maintain |
| Wetland testing | pH, temp, DO twice weekly; total N influent AND effluent, plus effluent nitrate, weekly to monthly |
| Wetland vegetation | Remove at end of growing season — the vegetation IS the sludge |
| Wetland burning | Wet burlap plus 5-gallon bucket over exposed pipe; permits required |
| Wetlands work best | As POLISHING behind activated sludge or lagoons |
| Wetlands and nitrogen | Not successful per this manual; data sporadic and inconsistent |
| Tertiary pond loading | 5–15 lbs BOD5 per acre per day |
| Facultative pond loading | 15–50 lbs BOD5 per acre per day |
Source and Notes
The uploaded manual
New Mexico Wastewater Systems Operator Certification Study Manual, prepared by the Water Utilities Technical Assistance Program (NMSU DABCC WUTAP) for the Facility Operations Section, NMED Surface Water Quality Bureau, Santa Fe, January 2005. 238 pages, 16 chapters. THE ENTIRETY OF THIS GUIDE IS DRAWN FROM CHAPTER 12 (TERTIARY TREATMENT), with loading rates from Chapter 5 (Wastewater Treatment Ponds) and cross-references to Chapter 13 (Nitrogen Removal) and Chapter 11 (Solids Handling).
Chapter 12 content used: the definition of tertiary treatment; the constructed wetlands sections covering theory of operation, subsurface and overland flow, effective uses, operations and maintenance, and process control testing; the phosphorus sections covering phosphorus as a nutrient, the need for removal, and the three removal system types — lime precipitation (including the three reactions and the equipment list), luxury uptake (including the 10 percent clarifier sizing), and aluminum sulfate flocculation and precipitation (including the 200–400 mg/L dose, the 0–0.5 mg/L result, the pH 6.0 optimum, jar testing, and the absence of economical alum recovery).
Studies cited WITHIN the manual and reproduced here as the manual reports them: W. Daniel Boivin, "Evaluation of Constructed Wetlands Performance in New Mexico," for the finding that subsurface flow constructed wetlands are incapable of removing the nitrogen in septic tank effluent to New Mexico Water Quality Commission standards; and long-term testing of wetland effluents by Michael Richard, Ph.D., on Colorado systems, showing periodic purging of nitrogen and phosphorus. NEITHER PRIMARY STUDY WAS ACCESSED — they are reported as the manual reports them.
The manual’s own further-reading reference: Operation of Wastewater Treatment Plants, 2nd Edition, Volume III (the Sacramento manual), cited for a more complete understanding of lime precipitation and phosphorus removal.
Cross-references to earlier guides in this series
The ALKALINITY guide — both lime and alum react with alkalinity, and in the alum case the alkalinity determines where in the 200–400 mg/L dose range you land. That guide treats alkalinity as a resource to protect for nitrification; this one treats it as a chemical demand to be paid for.
The INFLUENT VS EFFLUENT guide — the manual’s instruction to sample nitrogen at both influent and effluent connects directly to the percent removal framework, and the luxury uptake sidestream connects to the sidestream loading discussion.
The YOUNG VS OLD SLUDGE guide — luxury uptake depends on a healthy, controllable activated sludge process, so everything about sludge age control applies upstream of it.
The BARDENPHO and nitrogen material — Chapter 13 of this manual covers nitrification and denitrification in detail and would support a companion guide.
Caveats
| Item | Note |
|---|---|
| DATE | January 2005. Chemistry and process principles are durable; regulatory limits and state standards are not. |
| Scope | This guide covers Chapter 12 and the pond loading rates. Chapter 13 (Nitrogen Removal) is a separate body of material. |
| Wetlands assessment | The critical account of wetlands performance is THE MANUAL’S, based on New Mexico experience circa 2005. Design practice has developed since — particularly around aerated and hybrid wetlands. |
| Cited studies | Boivin and Richard are reported as the manual reports them. Primary sources not accessed. |
| Chemical dosing | The 200–400 mg/L alum figure is a general range. Actual dose is determined by jar testing on your own wastewater. |
| Regulatory | New Mexico Water Quality Commission standards and any NPDES limits are outside this manual and must be verified currently. |
| Not a design document | Operator guidance from a certification study manual. Process design requires an engineer. |
The most valuable thing in this chapter is its honesty about constructed wetlands. The theory is stated fairly and then measured against New Mexico field experience, and the gap is documented rather than glossed — including the line that THE VEGETATIVE GROWTH IS THE SLUDGE, and the finding that most systems required mechanical aeration after all.
The most useful operating numbers are on the alum side: 200–400 mg/L to reach 0–0.5 mg/L phosphorus, optimum around pH 6.0, jar tests to set it, and a filter afterward because the floc will not settle.
And the connection worth carrying into everything else: BOTH lime and alum consume alkalinity. What one guide in this series treats as a buffer to protect, this one treats as a reagent demand to budget for.
Where This Fits in Your Study
The full treatment process, step by step · Nitrification & denitrification · Alkalinity — the resource both lime and alum consume · Ponds & lagoons · The Grade 2 exam review
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