Leachate "Compliance" Only Treats the Water: Concentrate Lets Salts Circulate in the System

For leachate treatment, "compliance" is only half delivered in most projects: Nanofiltration and Reverse Osmosis drive COD, salinity, and color out of the produced water, yet push almost all of it into a concentrate stream accounting for 20%~30% of the original water volume; and "concentrate recirculation back to the landfill," an end-of-pipe outlet used for over a decade, has in principle been shut down in GB 16889—2024. The other half is "biodegradability": for every few years of landfill age, B/C drops from 0.6 to 0.1, while ammonia nitrogen accumulates to several thousand mg/L, the carbon-to-nitrogen ratio becomes imbalanced, dragging carbon source dosing and denitrification into an endless tug-of-war.

Gaowutong · Industrial Water Treatment Technology Series · For industry technical personnel · All data are annotated with public literature and engineering sources

Let us first draw the boundary clearly: leachate treatment is a "water—sludge—salt—gas" multiphase migration chain, and "compliance" describes only the "water" phase within it. MBR (Membrane Bioreactor) converts ammonia nitrogen and biodegradable COD into N₂ and CO₂ and truly sends them away; NF/RO (Nanofiltration / Reverse Osmosis) degrades nothing, merely moving pollutants from the produced water side to the concentrate side. Therefore, whether a chain holds does not depend on whether produced water COD is pressed down to 50 or 30 mg/L, but on where the concentrate ultimately ends up, in what form, and whether it can be disposed of compliantly.

I. Two Cliffs: Landfill Age Divides Leachate into Two Types of Water

Leachate water quality is not "a range," but a trajectory evolving with landfill age. The commonly accepted engineering classification is: below 3 年 is young (early stage), 3~5 年 is medium age, and above 5 年 is old age (late stage); what is continuously generated after closure basically belongs to the most difficult category to treat. The classification characteristic values given in the review by the Journal of Beijing University of Technology are as follows (typical values in parentheses):


Type	Age / a	pH	ρ(COD) / (g·L⁻¹)	B/C	ρ(NH₄⁺-N) / (mg·L⁻¹)	C/N Ratio
Early (young)	<5	6.5~7.5（7.0）	10~30（15）	0.5~0.7（0.6）	500~1000（700）	5~10（6）
Intermediate	5~10	7.0~8.0（7.5）	3~10（5）	0.3~0.5（0.4）	800~2000（1000）	3~4（3）
Late (aged/closed)	>10	7.5~8.5（8.0）	2000~tens of thousands of mg/L	0.1~0.2, closed-site water often <0.1	1000~3000（2000）, up to 10000 at the high end	<2 (severely imbalanced)

The early/intermediate data are from a review in Journal of Beijing University of Technology; the late-stage row integrates publicly available information from "Flocculation and Precipitation Methods for Landfill Leachate" and environmental impact assessments of closed-site projects.

Read vertically, and two lines running in opposite directions immediately emerge: COD and B/C head downward all the way, while ammonia nitrogen and salinity head upward all the way. This is the first cliff—the biodegradability cliff. In young leachate, volatile fatty acids (VFAs) can account for 50%~70% of total organic carbon, and microorganisms can "digest" it; in the mature stage, the readily degradable components are exhausted, leaving behind high-molecular-weight complex organics such as fulvic acid and humic substances, with B/C below 0.1, beyond the capability of ordinary Activated Sludge. In a certain closed landfill project 2018 年, actual measurements showed: pH 8.12, BOD₅ 50.9, COD 6.66×10³ mg/L (B/C≈0.008), ammonia nitrogen 2.31×10³, Total Nitrogen 3.72×10³ mg/L.

The second is the carbon-to-nitrogen ratio cliff. Ammonia nitrogen, unlike COD, does not decline with landfill age; it continuously accumulates during the methanogenic stage and actually becomes the highest single indicator in the mature stage. The publicly available data from the Laogang Phase IV landfill is a textbook sample: daily leachate generation of approximately 3000 m³, of which mature leachate accounts for 2700 m³, while fresh leachate accounts for only 500 m³; the weighted influent COD is approximately 10000, ammonia nitrogen approximately 3500, Total Nitrogen approximately 4300 mg/L, and the compiling party directly used the phrase "carbon-to-nitrogen ratio completely imbalanced."

The third is often overlooked, yet it is the root of the concentrate problem: salinity only goes in, never out. The conductivity of raw liquid is typically 10000~45000 µS/cm, and after membrane concentration, the concentrate can reach 40000~70000 µS/cm, with inorganic salts on the order of approximately 30000 mg/L. These substances do not participate in biological reactions, nor do they disappear on their own; they can only leave through one of "discharge, solidification, or transfer"—once "recharge" is chosen, they remain on-site and begin to circulate.

Figure 1　Schematic of biodegradability and ammonia nitrogen evolution with landfill age. The two lines form a "scissors gap" at 8~12 年: carbon source is depleted, ammonia nitrogen accumulates at high levels, and the carbon-to-nitrogen ratio becomes imbalanced. Thereafter, the goal shifts from "COD reduction" to "carbon source supplementation for denitrification + alkalinity supplementation to maintain nitrification" (illustrated by Gaowutong, sources see references [21][22][24])

II. MBR: Carbon Source and Alkalinity, a Pair of Interlocked Links

MBR plays the role of "main treatment," serving as the unit that truly removes pollutants rather than merely transferring them. CJJ/T 264—2017 and the draft for comments on the technical standard for leachate treatment provide highly consistent parameters:


Parameter	Standard Recommended Range	Engineering Experience Range	Underlying Constraints
MLSS	8000~15000 mg/L	12000~18000 mg/L	Enriches nitrifying bacteria; excessively high levels aggravate Membrane Fouling
Sludge Load F/M	0.05~0.3 kgCOD/(kgMLSS·d)	0.05~0.15	Low load accommodates recalcitrant compounds; excessively low causes sludge deflocculation
Nitrification / Denitrification Rate	Nitrification 0.02~0.08; Denitrification 0.04~0.13 kgN/(kgMLSS·d)	—	Determines tank volume; once load is exceeded, effluent ammonia nitrogen rises
SRT Sludge Retention Time	20~40 d	Aged water 45~60 d	Nitrifying bacteria generation time 15~20 d; short sludge age leads to washout
Water Temperature	20~35 ℃	In winter, insulation should maintain ≥15 ℃	<15 ℃ nitrification rate decreases
MBR Influent Conditions	COD ≤20000 mg/L; B/C ≥0.3; Ammonia Nitrogen ≤2500~3500 mg/L; BOD₅/Ammonia Nitrogen ≥5	—	Exceeding these requires upstream physicochemical load reduction
MBR Effluent (feeding spiral NF+RO)	COD ≤1200; BOD₅ ≤600; Ammonia Nitrogen ≤50; Total Nitrogen ≤100 mg/L; SDI₁₅ ≤5; Conductivity ≤20000 µS/cm	—	Gatekeeping for the membrane stage, not a discharge standard
Membrane Flux	External 60~70 L/(m²·h); Internal 8~20 L/(m²·h)	Internal typically designed conservatively at 8~15 LMH	Poor water quality requires flux lower than that for Domestic Sewage

Source: CJJ/T 264—2017 Section 4.2; "Technical Standard for Domestic Waste Landfill Leachate Treatment" (draft for comments) Section 5.4; engineering ranges are from publicly available technical proposals. Adoption shall be subject to bench-scale testing with the design water quality.

Carbon Source: The Most Expensive Spoonful in Aged Leachate

Young leachate naturally contains readily biodegradable organics; in aged leachate, the B/C ratio drops to only 0.1, and electron donors can only be purchased externally. The industry rule of thumb is: the carbon-to-nitrogen ratio (COD/Total Nitrogen) needs to be above 4; going higher will not further improve the denitrification rate; for aged landfills, the dosage often needs to be 4 times or even higher. Converted on a COD-equivalent basis, 1 kg of methanol is equivalent to approximately 1.4 kg of COD, and 1 kg of glucose is equivalent to approximately 0.6 kg of COD; methanol requires explosion-proof considerations, while glucose is relatively expensive.

Quantifying the cost of carbon sources reveals how "heavy" it is: in a publicly available calculation example, a leachate station at a landfill in western China, based on ammonia nitrogen of 700 mg/L and using glucose to raise CODCr by 5300 mg/L, increases the cost per ton of water by approximately 17.5 元; while the full-process operating cost of some incineration plants is only around 30 元/t — merely "carbon supplementation" alone could consume half the budget of the entire chain. In addition, because BOD₅ and Total Nitrogen are both difficult to measure, engineering practice often directly uses COD/ammonia nitrogen instead of BOD₅/Total Nitrogen: incineration plants have a B/C of approximately 0.5 and an ammonia nitrogen/Total Nitrogen ratio of approximately 0.8; landfills can have a B/C as low as 0.1 and an ammonia nitrogen/Total Nitrogen ratio as high as 0.9. The same phrase "carbon-to-nitrogen ratio of 4:1" does not represent the same actual demand for the two types of sites.

Alkalinity: The Second Deduction That Emerges After Carbon Source Dosing

Nitrification is an acid-producing process. According to general stoichiometry (calculated as CaCO₃), each 1 g of ammonia nitrogen oxidized consumes approximately 7.14 g of alkalinity, and each 1 g of nitrate nitrogen reduced produces approximately 3.57 g of alkalinity. Aged leachate has ammonia nitrogen of 2000~3000 mg/L, and the alkalinity demand for full nitrification is enormous; how much denitrification can replenish depends on how much carbon source is used to reduce nitrate nitrogen. Thus a closed loop forms: insufficient carbon source → incomplete denitrification → alkalinity cannot be replenished → nitrification is inhibited, pH drops sharply → ammonia nitrogen removal rate declines. A publicly available pilot test fully documented this chain: late-stage leachate (COD approximately 4.3 g/L, ammonia nitrogen 2.8 g/L) had a biodegradable COD/ammonia nitrogen of only 0.7; insufficient carbon source led to incomplete denitrification and inability to replenish alkalinity, and the ammonia nitrogen removal rate dropped from 99% to 92%; after continuous carbon source dosing, it recovered to 99.6%. Dosing carbon source appears to be for denitrification, but in essence it is simultaneously "replenishing alkalinity" for nitrification.

This is also why the upgrading project of Laogang Phase IV compared two routes side by side: Option 1 maintains 3200 m³/d, adds a 800 m³/d production line, and relies on carbon source dosing for denitrification, but the carbon source is expensive and the construction period is long; Option 2 maintains the original scale, adds stripping deammonification pretreatment before biological treatment to first reduce Total Nitrogen, then retrofits to two-stage AO, Nanofiltration, and concentrate minimization, and was recommended. The essence is: rather than using expensive carbon source to forcibly handle 4300 mg/L of Total Nitrogen, it is better to first "divert" part of the nitrogen through physicochemical means.

III. Nanofiltration and Reverse Osmosis: They Do Not Degrade, Only Transport

MBR effluent COD typically remains at the 600~800 mg/L level, which cannot meet the 100 mg/L limit, so advanced treatment must follow. The mainstream combination is "Nanofiltration + Reverse Osmosis" or "Disc Tube Reverse Osmosis (DTRO) + secondary Reverse Osmosis." The positioning must first be clarified: Nanofiltration selectively retains organics and high-valence salts, divalent salts, and some hardness; Reverse Osmosis retains almost all dissolved ions. One publicly available material description is: after biological effluent passes through Nanofiltration, it yields 85% of clear liquid based on the original water volume (COD approximately 120 mg/L, still not directly dischargeable) and 15% of concentrate; the clear liquid then passes through Reverse Osmosis to yield 60% of compliant clear liquid and 25% of concentrate; the two concentrate streams combined account for approximately 40% of the total treated water volume. If a high-recovery combination is used instead (DTRO single stage 70%~75%, two-stage series above 80%), the concentrate volume can be compressed, but the total pollutant mass remains unchanged — the "cleaner" the water, the "dirtier" the concentrate; this is an unavoidable material conservation principle.

The typical properties of the concentrate are quite consistent in public accounts:


Indicator	Typical Value of Membrane Concentrate	Meaning
Water Volume Proportion	20%~30% of the feed liquid (the combined "NF+RO" concentrate basis can reach about 40%)	The absolute amount that must be "digested"; "volume reduction" only changes the denominator
COD	Generally ≥5000 mg/L	Organic matter enrichment, dominated by refractory humic substances
BOD₅/COD	<0.1	Can no longer be treated biologically, which is the fundamental limitation
Conductivity	40000~70000 µS/cm	High salinity, high calcium and magnesium, highly prone to scaling
Inorganic Salt Content	On the order of about 30000 mg/L	Based on the survey scope of the standard drafting group
Color / Heavy Metals	Color 50~1500 times, brown-black; high heavy metal and humic substance content, mainly in complexed form	Humic acid complexes with heavy metals, increasing toxicity and making removal by conventional precipitation difficult

Source: Guangzhou Urban Management Bureau, "Characteristics of Landfill Leachate Membrane Concentrate Generation and Discussion of Disposal Methods"; interview with Liu Yuqiang, drafter of GB 16889—2024 (China Environment News, 2024-10).

Substituting back into the overall picture yields a hard order-of-magnitude judgment. The estimate given by Liu Yuqiang, a drafter of GB 16889—2024, is: landfills nationwide generally adopt Nanofiltration + Reverse Osmosis to meet standards, this process generates 20%~30% concentrate, and based on this it is estimated that up to 500 万 tons of concentrate are generated nationwide each year; its BOD/COD is less than 0.1, and inorganic salts are about 30000 mg/L. For many years, "recirculation has mostly been adopted, which cannot fundamentally remove pollutants." This is the technical basis for revising the discharge method in the new version of the standard.

Figure 2　Typical process chain of "MBR + Nanofiltration/Reverse Osmosis" and the destination of the concentrate. The green box (MBR) is the stage where pollutants are truly degraded, while the orange boxes (NF/RO) are the stages where pollutants are transferred; viewing these two types of units separately makes the boundaries of the process chain clearer than comparing removal rates in a parameter table (illustrated by Gaowutong, sources see references [4][7][11][12])

IV. Five Routes and Hard Constraints for Concentrate Disposal

Concentrate disposal is the only link in this chain with "no standard answer." Five main routes have emerged in China, each constrained by a physical or compliance limitation.


Route	Core Action	Pollutant Fate	Hard Constraints
① Recirculation to Landfill	Concentrate is sprayed or injected into the waste mass, relying on adsorption and biodegradation	Remains on site, collected again by the drainage system	GB 16889—2024 in principle does not permit direct recirculation; salts and refractory substances continuously accumulate, threatening the stability of the waste mass
② Evaporation (MVR / Submerged Combustion SCE / Low-Temperature Evaporation LTE)	Water is recovered as distilled water, salts and organics remain in the residual liquid	Distilled water is reused; mother liquor is dried or outsourced	High investment and energy consumption; calcium and magnesium scaling and organic foaming are the main obstacles; the mother liquor still has 25%~45% to be treated
③ Incineration Synergy (Furnace Re-injection / Lime Slurry Preparation / Fly Ash Solidification Make-up Water)	Sprayed into the waste incinerator or used as slurry make-up water	Enters flue gas and fly ash, solidified with fly ash	Sulfides and chlorides cause progressive corrosion to heating surfaces; poor atomization affects combustion; Ca(OH)₂, ammonia water, and activated carbon consumption increase
④ Advanced Oxidation (Fenton, etc.)	Free radicals break down refractory organics	Organics are partially mineralized or converted to biodegradable intermediates	Large amounts of chemicals and iron sludge, high cost; oxidation efficiency is inhibited under high-salinity conditions; difficult to completely mineralize when used alone
⑤ Salt Fractionation and Crystallization	After evaporation and concentration, NaCl, KCl, etc. are precipitated according to solubility	Solidified into industrial salt, the only path for salt to leave the site's water system	High requirements for upstream softening and salt fractionation; mixed salts have no value; high investment

Among the five, ① was once the most cost-saving, and it is precisely the one the new standard aims to shut down. Its problem is not "poor effectiveness," but no outlet: after recirculation, salts and refractory substances re-enter the leachate and are concentrated again, with concentrations rising round after round. Patent CN119954307A provides evidence: leachate plants using RO membranes "recirculate to the equalization tank, causing the chloride ion concentration in the equalization tank to exceed 5000 mg/L, basically in the range of 7000~10000 mg/L", and these high-salinity waters have become a "potentially significant environmental pollution risk."

Figure 3　Comparison of the closed-loop concentrate recirculation and the full-quantification open loop. The red dashed line in Figure A forms a closed loop, i.e., "salts cycle endlessly within the system"; the endpoint in Figure B is solid salt or incineration products, and pollutants no longer return to the raw water. GB 16889—2024 tightening recirculation is essentially removing this dashed line in Figure A from the compliance pathway (drawn by Gaowutong; chloride data see reference [17], route sources see references [10][11][14])

V. The Real Ledger: 9 Sets of Public Engineering Data

The following table is entirely sourced from publicly available literature, government public documents, and public engineering reports. It is only compiled and aligned without any extrapolation.


Project / Scale	Water Quality Characteristics	Process Chain	Effluent / Results	Source
Shenzhen Bao'an Waste Incineration Power Plant 1745 m³/d (incineration plant 1260 + landfill 350 + others)	Incineration plant leachate blended with landfill leachate; landfill water has higher salinity	Anaerobic + MBR + NF (humic acid extraction) + RO + Evaporative Crystallization Salt Separation (480 m³/d, crystallized salt approx. 25 t/d)	Condensate TDS <30, COD <10 mg/L fully reused; NaCl purity >97.5% (GB/T 5462—2015), KCl >97% (GB/T 7118—2008); 2013 acceptance, 2016 commissioning	Reference [14]
Laogang Phase IV Landfill 3200 m³/d	Aged water 2700 + fresh water 500 m³/d; COD approx. 10000, ammonia nitrogen approx. 3500, Total Nitrogen approx. 4300 mg/L; detected ammonia nitrogen 2000~2800 mg/L; carbon-to-nitrogen ratio completely imbalanced	① Two-stage AO + carbon source dosing + Nanofiltration + concentrate reduction; ② stripping deammonification before biological treatment + two-stage AO + Nanofiltration + concentrate reduction (recommended)	No publicly available effluent specifications (scheme comparison document)	Reference [13]
A landfill in Liaoning, capacity expansion adding 600 m³/d	Accumulated leachate from an aging landfill	Homogenization + MBR + Nanofiltration + Reverse Osmosis; NF concentrate "reduction + coagulation sedimentation", RO concentrate "low-temperature evaporation + drying" for full volume treatment	Effluent COD <20, ammonia nitrogen ≤5, Total Nitrogen ≤10 mg/L, superior to GB 18918 Grade 1A; cost approx. 125 元/m³	Reference [16]
A waste incineration power plant in Guangzhou 300 m³/d, zero discharge	Incineration power plant leachate	UASB — external MBR — NF/RO	COD ≤13.9, ammonia nitrogen ≤0.69, Cl⁻ ≤175.19 mg/L, meets GB/T 19923—2005 circulating cooling water make-up; removal rates COD/NH₃-N/conductivity 99.98%/99.97%/95.36%; clear liquid reused, concentrate reused for lime slurry preparation	Reference [7]
Synergistic treatment of incineration plant leachate and kitchen waste biogas slurry at a certain plant 750 m³/d	Mixed wastewater of leachate + kitchen waste biogas slurry	Deslagging + equalization tank + UASB + (two-stage A/O + external UF) MBR + NF + RO	COD, ammonia nitrogen, Total Nitrogen stably below 20, 3, 10 mg/L; removal rates 99.98%/99.96%/99.76%; operating cost 33.104 元/t	Reference [9]
Qingdao Xiaojianxi Comprehensive Disposal Park, concentrate 500 t/d	Aged leachate membrane concentrate, high salinity, refractory organics	Advanced flocculation (OLC) + chemical softening + silicon carbide membrane + MVR evaporation + drying reduction + incineration synergy	Treatment capacity 300→500 t/d; evaporation mother liquor concentration rate approx. 25%, drying mother liquor approx. 45%; annual disposal cost savings approx. 1120 万 yuan, carbon reduction approx. 5200 tCO₂e; has been extended to Beijing Anding Landfill and others	Reference [10][11]
High-speed circulating evaporation of concentrate promoted in Shandong, Heilongjiang and other regions	Membrane concentrate enriched after biological treatment + NF + RO	High-speed circulating evaporation (MVR principle circulating secondary steam) + high-velocity forced circulation + online cleaning	Distilled water can meet GB/T 19923 boiler make-up water standard for reuse; investment 4~6 万 yuan/t, operation 40 元/t	Reference [15]
"Zero-Waste City" advanced applicable technology: full-volume treatment of leachate concentrate	Membrane concentrate	TUF softening membrane (35~38 bar) + DT membrane (45~55 bar) + MVR evaporation (95~98 ℃) + RO (35~38 bar)	Effluent meets GB 16889—2008 Table 2; sludge volume ≤ 6% of concentrated treatment volume; total investment approx. 750 万 yuan, concentrate treatment cost approx. 160 元/t	Reference [19]
New construction at an incineration plant in Jiangsu, 100 m³/d stage	Incineration plant leachate; DTRO influent TDS controlled at 80000~120000 mg/L	Sand filtration + bag filtration + acid/alkali adjustment → DTRO (two-stage skid-mounted) → MVR (10 m³/d concentrate)	Effluent meets GB 16889—2008 Table 2; MVR reduction ratio 90%~92%, concentrated salt residual liquid reduced to 2%~3% of influent for hazardous waste disposal; MBR route 8~16 元/t, full-volume zero discharge 22~30 元/t, cost per ton of water 15~25 元/t	Reference [20]

Reading horizontally, the pattern is clear: the full-process cost of incineration plant leachate (including kitchen waste synergy) is mostly 15~33 元/t; for the "full-volume + evaporation" route of aged landfill leachate, once concentrate disposal is factored in, the cost quickly jumps to 125~160 元/t. The gap is not in MBR and NF/RO, but in the last cell. This is also the core judgment of this article: "membrane" is not the protagonist, "concentrate outlet" is.

VI. Process Comparison: Five Concentrate Routes Side by Side


Route	Volume Reduction Effect	Pollutant Fate	Cost Magnitude (Public Basis) and Preconditions
Recirculation to Landfill	No volume reduction	Remains within the landfill body and leachate system, with salt accumulation	Lowest investment; the new standard in principle no longer permits direct recirculation, and it may only serve as a transitional measure without affecting landfill body stability
Incineration Synergy	Liquid reduced to zero	Enters flue gas and fly ash, then solidified or landfilled with fly ash	Can "directly utilize the vast majority"; the cost is heating surface corrosion and increased flue gas consumables; a supporting incinerator is required
MVR / Low-Temperature Evaporation	Distillate recovery, mother liquor concentration ratio approximately 25%~45%	Salts and organics enriched in mother liquor, then dried or outsourced for disposal	High-speed circulating evaporation: investment 4~6 万 yuan/t, operation 40 元/t; Liaoning case full process 125 元/m³; low-cost steam or waste heat is required
Advanced Oxidation (Fenton, etc.)	No volume reduction, mainly improves biodegradability	Organics partially mineralized or converted to biodegradable intermediates	Higher cost of chemicals and iron sludge; more reasonable as pretreatment for evaporation or biological treatment
Salt Fractional Crystallization	Water reuse, salt solidification	The only pathway that removes salt from the site water system, with industrial salt available for external sale	Shenzhen Bao'an: NaCl 7 kg/m³ (approximately 180 元/t), KCl 4 kg/m³ (approximately 2500 元/t); pretreatment equivalent to raw liquid 3~4 元/m³, evaporation crystallization approximately 10 kWh/m³; high requirements for upstream softening and salt separation

VII. Three Definitions That Need to Be Clarified on the Spot

Fact Check 1: The other side of the "cost-saving" leachate concentrate recirculation is the compound accumulation of chloride ions.
Recirculation was widely adopted in the past, and engineering documents often state "leachate concentrate recirculated to the landfill area." From a closed-loop perspective, it removes no pollutants: salts and recalcitrant substances re-enter the leachate, are collected again, and are concentrated again, with concentrations rising round after round. Field data (Patent CN119954307A) show that after recirculation, Cl⁻ in the equalization tank often exceeds 5000 mg/L, mostly in the range of 7000~10000 mg/L. Chloride ions have well-established engineering empirical thresholds for inhibiting biological treatment: Cl⁻ >2000 mg/L activity is inhibited and COD removal rate drops significantly; >5000 mg/L osmotic pressure can increase to 10~30 atmospheres; >8000 mg/L sludge bulking, massive foaming, and successive microbial death. Recirculation saves the current disposal cost but pays with continuous degradation of biological treatment capacity. The basis for GB 16889—2024 tightening restrictions on recirculation is precisely what the drafting committee found in their research: "salts will continuously accumulate, leading to reduced efficiency of the biological system and clogging of the membrane system, and in severe cases causing system breakdown," as well as "recirculation will seriously affect the stability of the landfill mass, causing safety risks such as slope sliding."

Fact Check 2: "Permeate meeting standards" and "concentrate destination" are two separate matters, and standards have long only addressed the former.
Over the past decade or so, acceptance criteria focused on the permeate side: effluent COD ≤100, ammonia nitrogen ≤25 mg/L was considered "meeting standards." But according to the drafters' explanation, the original standard "stipulated that water pollutants are only allowed to be discharged to the water environment after treatment meets standards," which objectively pushed all projects toward "NF + RO," thus generating 20%~30% leachate concentrate. The revision addresses both aspects: first, a new indirect discharge (sewer connection) pathway for leachate is added, with conventional pollutants complying with GB/T 31962, Class I heavy metals having identical indirect and direct limits to prevent dilution discharge, and requiring separate drainage pipes, online monitoring, daily manual monitoring, and contracts with wastewater treatment plants; second, direct recirculation of leachate concentrate is in principle not permitted. Therefore, any engineering document that still states "leachate concentrate recirculated to landfill area" should have its compliance re-verified.

Fact Check 3: The three "meeting standards" limits differ by 5~10 times and cannot be used interchangeably.
At least three different criteria exist simultaneously for leachate, and the most common mistake is treating them as the same thing:
① GB 16889—2008 Table 2 (direct discharge): COD ≤100, ammonia nitrogen ≤25, Total Nitrogen ≤40 mg/L;
② GB 18918—2002 Grade 1A: COD ≤50, ammonia nitrogen ≤5(8), Total Nitrogen ≤15 mg/L, significantly stricter than ①. A landfill project in Liaoning 600 m³/d implements Grade 1A, stably achieving COD <20, ammonia nitrogen ≤5, Total Nitrogen ≤10 mg/L;
③ GB/T 31962 sewer connection criteria (newly added in the 2024 version): commonly cited limits are CODcr ≤500, ammonia nitrogen ≤45, Total Nitrogen ≤70 mg/L, with the grade determined by the sewer connection agreement.
For the same phrase "meeting standards," ① and ③ differ by 5 times in COD and nearly 2 times in ammonia nitrogen; if Grade 1A is also considered, ③ and ② differ by 10 times in COD. Before discussing "leachate treatment costs," one must first ask which standard tier applies—designing only to sewer connection criteria will result in significantly lower costs (the drafters also explained that the new indirect discharge provision was made "from the perspective of technical economy and feasibility"); if the target is Table 2 or Grade 1A, neither advanced treatment nor concentrate disposal can be avoided.

VIII. Engineering Truths

Truth 1: Determine the concentrate destination first, then design the upstream process chain—reversing this order will definitely require rework.Where the concentrate goes determines whether NF/RO is needed, whether softening is required, how large the evaporator should be, and whether there is an incinerator available for synergistic disposal. If you first configure the membrane system for "permeate meeting standards" and then look for a concentrate destination, the result is ever-accumulating leachate concentrate.

Truth 2: The carbon source dosage for aged leachate will be severely underestimated if calculated using incineration plant coefficients.In engineering practice, COD/ammonia nitrogen is commonly taken as "4 or above," but incineration plants have a B/C ratio of about 0.5, while landfills can be as low as 0.1; the same phrase "carbon source added at 4 times" often translates to higher amounts for aged landfills. Carbon source is a continuously consumed item, and if this is off, the whole-life-cycle cost will be off.

Truth 3: Adding carbon source is not just for denitrification—it is simultaneously "replenishing alkalinity" for nitrification.Nitrification consumes approximately 7.14 g alkalinity per 1 g of ammonia nitrogen oxidized, while denitrification produces approximately 3.57 g per 1 g of nitrate nitrogen reduced. If carbon source is insufficient and denitrification is incomplete, alkalinity cannot be replenished, the pH in the nitrification tank drops, and ammonia nitrogen removal rate declines accordingly. Accounting for carbon source merely as a "denitrification chemical cost" underestimates it.

Truth 4: Bypass connections for "process switching" must be reserved during design.Water quality drifts unidirectionally with landfill age, and a process designed today for new landfill water quality may be completely mismatched a few years later. Many projects meet standards initially but lose control after several years of operation—the root cause is the failure to reserve bypasses and standby units. The cost of reserving connections is far lower than shutdown for retrofitting.

Truth Five: For the evaporation route, the "volume reduction ratio" is more worth negotiating than the "evaporator model." Raising the MVR volume reduction ratio from 85% to 92% increases installed capacity by only about 15%, but can save about 40% in outsourced disposal costs. The effectiveness of front-end softening and advanced flocculation directly determines the back-end disposal cost and equipment investment—this is precisely the logic behind the Qingdao model placing "advanced flocculation" before MVR.

Truth Six: The "cost items" of evaporation and incineration synergy must be clearly written into the contract first. Re-injection into the furnace brings progressive corrosion of heating surfaces, combustion instability when atomization is poor, and increased consumption of calcium hydroxide, ammonia water, and activated carbon to keep flue gas compliant. If not accounted for at the planning stage, these will come back as maintenance and consumable costs after commissioning.

IX. References

GB 16889—2008 "Standard for Pollution Control on the Landfill Site of Municipal Solid Waste".
GB 16889—2024 "Standard for Pollution Control on the Landfill Site of Municipal Solid Waste", Ministry of Ecology and Environment, implemented on 2024-09-01 (newly added indirect discharge to sewer; in principle, direct recirculation of concentrate is not permitted).
GB 18918—2002 "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant".
GB/T 31962—2015 "Water Quality Standard for Sewage Discharged into Municipal Sewers".
CJJ/T 150—2023 "Technical Standard for Leachate Treatment of Municipal Solid Waste".
CJJ/T 264—2017 "Technical Specification for Membrane Bioreactor Treatment System of Municipal Solid Waste Leachate".
"Technical Standard for Leachate Treatment of Municipal Solid Waste" (Draft for Comments), Ministry of Housing and Urban-Rural Development.
UASB-MBR-NF/RO process for treating landfill leachate from incineration power plants [J]. Industrial Water Treatment, 2022, 42(8).
Case study of synergistic treatment of landfill leachate and kitchen waste biogas slurry from incineration plants [J]. Henan Chemical Industry, 2023, 40(12): 45-48.
Public report on full quantitative disposal of concentrate at Qingdao Xiaojianxi, Qingdao Daily / Guanhai News, 2024-11-30.
Characteristics, disposal methods and discussion of leachate membrane concentrate, Guangzhou Urban Management and Comprehensive Law Enforcement Bureau.
Exclusive interview with Liu Yuqiang and Liu Jianguo, drafters of GB 16889—2024, China Environment News, The Paper, 2024-10.
Analysis of new leachate treatment technologies at Laogang Landfill, Xiong Jianying (Shanghai Municipal Engineering Design Institute), Solid Waste Network.
Public technical report by the Chief Engineer of Shenzhen Energy (zero liquid discharge and evaporative crystallization salt separation for Shenzhen Bao'an leachate).
High-speed circulating evaporation treatment of landfill leachate concentrate, National Comprehensive Service Platform for Ecological and Environmental Technology Transfer, 2023-10-25.
Engineering case of full quantitative treatment of leachate from aging landfills to meet high discharge standards [J]. Environmental Sanitation Engineering, 2026, 34(3).
Microbial maintenance and full quantitative treatment method for biochemical treatment of high-salinity landfill leachate, Chinese Invention Patent CN119954307A.
Advanced and applicable technologies for "Zero-Waste City" construction: full quantitative treatment technology for leachate concentrate, Environmental Development Center of the Ministry of Ecology and Environment.
Brief analysis of research and application status of landfill leachate treatment processes [J]. Journal of Beijing University of Technology.
Flocculation and sedimentation methods for landfill leachate, brief discussion on landfill leachate, Wastewater Treatment Engineering Network, etc.
Environmental impact report for the closure project of the domestic waste landfill in Qingshui Village, Baita Township, Xingcheng City, government public document.
Experience in carbon source dosing and C/N ratio measurement in leachate operations, compiled from Tsinghua University and CAEPI leachate operations lecture; alkalinity research in A/O pilot testing of mature leachate, China Water Network; nitrification alkalinity consumption of 7.14 and denitrification alkalinity production of 3.57 g CaCO₃/g N are general theoretical values.

Gaowutong · Industrial Water Treatment Technology Series · All data in this article are from public literature, national standards, and public engineering cases; for specific project design, please refer to water quality bench tests and the actual conditions of your plant.

Leachate "compliance" only treats the water: the concentrate keeps salts circulating within the system.