operation oaxaca: i found a compass.

the target market rabbit-hole (019)

Carlos Manuel Jarquín Sánchez
8 min readFeb 24, 2024

this is carlos.

completing some things up.

modifying the purchasing products.

it’ll be better to purchase magnesium hydroxide and aluminum hydroxide instead of nitrate.


hydroxide ions are present (OH-) when they’re attached to the magnesium/aluminum ions.

magnesium hydroxide looks like: (Mg(OH)2)

aluminum hydroxide looks like: (Al(OH)2)

but if you want to separate the hydroxide ions from the soluble metal ions…

add an acidic substance for the anionic hydroxide groups to react with (OH-).

we can use hydrochloric acid (HCl).

when we add the acid onto the aqueous solution of magnesium hydroxide and/or aluminum hydroxide, we get:

Mg(OH)2 ​+ 2(HCl) → Mg²⁺ + 2Cl⁻ + 2(H2​O)

we would need two HCl molecules… as one hydrogen ion is released per HCl molecule.

but anyway, that’s not the focus.

i’ve decided where to lean on the target market.

and as expected, i concluded by the following words:

economics first. everything else second.

imma focus on heavy metal ions recovery from mining sludge/wastewater (typically lead, copper, aluminum, silver, gold, and more).

there are metal ions that can be recovered and made into profit.

that’s a good company.

but if i did it with kitchen sinks, hell nah.

who got time to go to a million homes and collect their valuables??

if it’s already there, make sure it stays there.

so now, let’s nose-dive into the market.


when the sludge is disposed of from the treatment plant…

that is about 40–60% of the treatment plant’s costs!

ye, really.

it depends on the percentage due to:

  • size of the treatment plant's
  • initial wastewater characteristics

but how do we usually dispose of the sludge?

two big options:

  • off to landfill
  • reuse as fertilizer

but transport costs increase with more sludge amount (i.e. heavier weight, gasoline, distance to landfill), & with chemical precipitation costs.

but as we start increasing the environmental costs for such behavior, traditional methods extract more money out of the plant than what’s going in.

example: treatment plant managers who relied on the sludge-to-fertilizer route as a way to avoid disposal fees now must figure out what to do with that sludge.

but here’s another catch:

each wastewater treatment plant needs its tailor-made system.

aka: there’s no ‘one size fits all’ solution.

however, there exist methods to mitigate the amount of sludge created.

they include processes such as:

  • chemical
  • thermal
  • biological

how do we pick?

by deciding: “what do we wanna do with the sludge?”

the expenditure sheet.

so one of the easy solutions to solve the build-up of contaminated wastewater from mines is to outsource their problem…

most likely to another company.

but disposing of wastewater sludge can make up 40–60% of a treatment plant’s costs. (the percentage depends on the size of the plantations)

that includes:

  • transportation
  • costs of landfill dumping and/or
  • contracts with third-party organizations to deal with the waste

and the landfill can have its rising costs of landfill dumping… where most sludge ends up anyway.

but for proof…

in europe, the average cost of sewage sludge disposal ranges between EUR 160 and 310 per ton of dry sludge. (USD 173.38–335.93)

and the total annual operating cost, including thermal and electrical energy costs, equaled EUR 833,000. (USD 902,680.45)

EUR → euro

and guess what?

after transportation costs…

energy consumption is between 7% to 33% of the total operating costs of wastewater treatment. that makes it the second largest cost factor.

so, the more sewage sludge is produced, the more energy is required for the sludge treatment.

so when it comes to mining and sludge wastewater treatment plants…

this is the solution:

use a technology (or more) to reduce excess sludge production while limiting the energy consumption of the wastewater treatment plant.

ok… so what’s being done so far?

a common move is removing the extra water from the sludge before transported to its respective treatment plant.

why spend more on transporting the waste to move water??? i thought we only wanted to move waste only.

these are known as hydroclones.

but how do the metal precipitation treatment plants work?

how a metal precipitation treatment plant works

and the handling of the sludge is unfavorable, economically.

the combined operation of dewatering and hauling vacuum-filtered sludge, the average cost per dry ton was USD 87 (average).

specific example:

an annual cost of USD 160,520 for 970 dry tons of sludge…

which can lead up to USD 165 per dry ton.

and the energy use intensity for an operating wastewater treatment plant is about 50 kBtu/gallons per day.

kBtu → kilo british thermal units

british thermal units → a unit of energy equal to the amount of heat required to raise the temperature of one lb. of water by 1°F.

the trucks used could range from USD 2400 — 5200. depends if it’s a tractor or a truck.

case studies. (usa)

case #1: louisville, kentucky.

treats water for about 500,000 people.

the wastewater treatment plant is about three miles from the landfill site (where they dump the sludge).

average trip time from the plant to the landfill is between 30–45 minutes.

all costs, including:

  • personnel (truck driver, supervisor of landfill, vacuum filter operators, and laborers)
  • transportation
  • cost to buy truck
  • chemicals/materials
  • maintenance of equipment

all that costs about USD 229,070.00

and all the sludge that’s hauled annually, on average is about 4590 dry tons.

divide the money by the tons…

and it gives us about USD 50 per dry ton of mining sludge.

case #2: rochelle, illinois.

it has a population of about 9000 people, and about 75 miles west of chicago.

the activated sludge plant in rochelle using the waste and treating it for the sludge to be applied in farmland.

but in that town, there’s a farmer that takes care of the sludge before it goes the sludge plant. the farmer would use the sludge for his land.

from the wastewater plant to the farms, it’s about 13 miles round trip consisting of 25–30 minutes.

average of 6 or 7 loads will be transported 5x/day for a five-day week from the plant operations.

the farmer uses about 25 wet tons/acre (or 6 dry tons/acre.)

sludge disposal on farmland for rochelle, illinois costs about USD 89 per dry ton…

and USD 75 per dry ton is specifically used for dewatering operation costs.


the truck/machines costs are about USD 62,780.

personnel is about USD 31,850.

electricity at USD 0.0239/kwh is about USD 18,320.

total annual costs are about USD 174,490.00

(if we include administrative overhead, repairs, water costs, and more)

the total amount of tons produced per year (on average) is about 1950 dry tons.

that’s where we get USD 89/dry ton.

case study #3: toledo, ohio.

it’s about 50 miles south of detroit, michigan.

the wastewater treatment plant in toledo serves about 500,000 people.

dewatered sludge is typically handed over for farmland applications.

the company that handles the sludge is “soil enrichment materials corporation (semco)”.

it has contracted about 867 acres of farmland in wood county, ohio, but so far, it has about 415 acres of received sludge… at no cost to the farmers in that county.

and land that has received sludge was used for the production of corn, soybeans, and hay.

drive time from the plant to ‘semco’ is a round-trip of 45.2 miles and 2.5 hours.

the annual sludge treatment and handling costs are estimated to be about 40% — 50% of the wastewater plant operating costs.

the annual costs of trucks, equipment, and vacuum filters are about USD 500,000.

labor, chemicals, and power for the vacuum filters is about USD 730,000.

semco takes care of hauling and spreading the sludge onto the farmland, not the city of toledo.

but still…

sludge hauling at (USD 2.92/wet ton) is about USD 237,000.

sludge spreading at (USD 3.24/wet ton) is about USD 263,000.

so the annual total cost of the treatment plant (including administrative overhead) is about USD 1,903,000.

and 16,250 dry tons were produced this year.

divide the total cost by tons… and we got USD 117/ton.

the top three heavy metals were:

  • aluminum (2,200–53,500 ppb) | 32 ppb per dry ton
  • calcium (60,000–135,000 ppb) | 204 ppb per dry ton
  • iron (22,000–101,000 ppb) | 142 ppb per dry ton

case study #4 is belleville, illinois.

population is about 41,700 people.

it’s located ~15 miles southeast of st. louis, missouri.

liquid sludge is also applied for farmland uses.

farmers who are between 5–10 miles from the wastewater treatment plant who want to use the sludge on their land can ask for it and they’ll get their sludge.

total sludge generated in one day is ~33,000 gallons/day.

sludge that leaves the treatment plant is ~15,000 gallons/day… or 2.4 dry tons of sludge/day.

the transport vehicles purchased were two 2,000-gallon trucks.

vehicle costs were ~USD 18,600.00

total operations budget annually is ~USD 325,549.00

in this town, the salaries and wages were >65% of the plant’s cost.

at the time, they had 22 full-time employees for the city’s water treatment plant.

but this plant did air-dried sludge & liquid sludge.

the total cost for air-dried sludge disposal annually was USD 17,130.00

the total cost for liquid sludge disposal annually was USD 12,060.00

air-dried sludge produced 500 dry tons.

so did liquid sludge.

so the average cost for air-dried sludge was USD 34/dry ton.

so the average cost of liquid sludge was USD 24/dry ton.

and the top three heavy metals present (on a dry-weight basis) were:

  • iron (33,510 ppm)
  • aluminum (5,380 ppm)
  • calcium (20,660 ppm)

case study #5 is danville, virginia.

population is ~49,000.

it’s located about 50 miles north of greensboro, north carolina.

liquid sludge will be applied to farmland surrounding the perimeter of the southside wastewater pollution control facility.

the city has 19 farms nearby, totaling 4200 acres of land.

any farmer within a nine-mile radius could request liquid sludge to be used on their land.

and nearby, there’s a textile mill factory where secondary waste sludge treatment occurs.

and the “dan river mills’ textile” discharges ~60% of the waste into the dan river.

14 loads of sludge per day are hauled in & out of the plant.

it takes about 10 minutes to both load/unload cargo.

for the annual cost to run the mine…

the piping, trucks, and capital… the cost annually was USD 14,360.00

personnel costs are USD 9,750.00 (drivers, technicians, operators, administrative overhead, etc.)

additional costs like depreciation, electricity, maintenance, and operations were USD 16,080.00

total cost annually was USD 33,480.00

total sludge hauled annually is an average of 1,490 dry tons.

divide total cost by tons… we get USD 22/dry ton.

the top three heavy metals on a dry-weight scale were:

  • copper (247 ppm)
  • lead (178 ppm)
  • zinc (350 ppm)

i know that does not represent all places.

i just selected four random locations and collected the data i needed to present my case.

and what’s the case?

that the sludge has metals in there.

if only there was a process to remove them from the sludge on-sight…

think of all the valuable metals we’re letting sit in the landfills.

and that’s why imma go to the sludge filtration market.

now, a deeper dive, round two.

see you tomorrow on how sludge filtration works.

© 2024–2100 by Carlos Manuel Jarquín Sánchez. All Rights Reserved.