Heinz-Peter Mang
Beijing Century Green Environmental Engineering & Technology Ltd., which operates night-soil treatment plants. Treating waste is set to be a growing area of business, Zhang said....unrecyclable solid material like tissue paper and plastic bags is separated, explained Zhang Hui, the plant’s manager.
The rest then goes for separation: the solid waste is propelled into a compost wing to ferment at 60 degrees Celsius [140 F] for 10 days. The process kills harmful bacteria and ascaris eggs — parasitic roundworms that infect humans — and turns the excrement into rich fertilizers for trees and vegetables.
because Chinese often cook with fresh ingredients, the overall mix of waste tends to be wetter than in Europe, Mang said. “It’s very humid so it needs too much energy to incinerate, that’s why you can’t copy the European model,” he says with a hearty chuckle.
Storing the urine - no longer smells after a few months and has no corrosive effect. OK but after a year it does smell like ammonia!
When a stored urine sample sits out for a long time, bacteria in the environment break down urea into ammonia, creating a strong ammonia smell...When exposed to air and ambient bacteria over time, that urea converts directly into ammonia gas
Urine needs to be stored for 1 to 6 months in a sealed container to be safe as a fertilizer, depending on who will eat the crops...Pathogen Die-Off: Urea in stored urine naturally breaks down into ammonia over time, raising the pH above 9.
Yes, urine that has converted to ammonia can still be used as a fertilizer after you dilute it. [1]
How Urine Changes
- Fresh vs. Aged: Fresh urine contains urea. As it sits, natural enzymes convert that urea into ammonia, which causes a strong smell.
- Nutrient Value: Aged or ammonia-rich urine still contains valuable nitrogen, phosphorus, and potassium that plants need.
- Alkaline stabilization is primarily designed to eliminate pathogens rather than transform organic contaminants, a distinction frequently overlooked in sludge management practice. For PCBs, PCDD/Fs, and PFAS, lime treatment offers no meaningful reduction. Overall, liming contributes minimally to organic contaminants mitigation and requires complementary treatment technologies to ensure the safe agricultural reuse of SS [178,179].... liming neutralizes acidity and immobilizes metals, enhancing sludge safety for soil application [188]. SS composting systems often experience early-phase acidification due to organic acids accumulation, which inhibits microbial activity and delays thermophilic conditions. To counteract this, alkaline additives such as lime are applied to buffer pH and accelerate decomposition. Quicklime is particularly effective as it raises pH, generates heat, reduces odor, suppresses pathogens and stabilizes metals, thereby enhancing sludge composting
https://www.mdpi.com/2076-3417/16/10/4805#
According to Chowdhury et al. [229], inactivation, or destruction, is expected if all compost particles sustain temperatures over 55 °C for at least 3 days under static or in-vessel composting systems, or for 15 days under windrow composting with turnings to ensure the uniformity of the temperature over the material under the composting process.
The addition of lime in SS raises the pH, which, in turn, reduces the metals’ solubility and mobility, making them less available for leaching and for organism absorption [310,311]. The procedure is also effective in destroying pathogens such as Escherichia coli, eliminating bacterial and viral pathogens by up to 99% [115,312,313,314]. At the end of the process, the stabilized SS has properties that make it suitable for a wide range of applications, namely agriculture, as an alkaline amendment,
Calcium oxide rapidly increases pH above 12 through an exothermic reaction, ensuring strong pathogen reduction and enhanced dewatering but requiring careful handling. Hydrated lime also generates high alkalinity (pH 10–12) without heat release, offering effective and safer stabilization
Before composting begins, the thick, high-pH sludge is mixed with massive quantities of coarse, carbon-rich bulking agents like wood chips, sawdust, or straw.
[1, 2] - The Mixing Effect: These amendments have a naturally lower or slightly acidic pH, which instantly dilutes the alkalinity of the lime.
- Carbonation: As the mixture is exposed to the air, the lime (calcium hydroxide) reacts with ambient carbon dioxide (CO₂) to form calcium carbonate (limestone). This chemical process naturally pulls the pH down closer to a neutral range (7.5 to 8.5) where composting microbes thrive. [1, 2]
2. Immediate Re-Inoculation
While the native aerobic bacteria in the sludge may have been wiped out, no compost pile starts in a sterile bubble.
- The bulking agents (wood chips, yard trimmings) are already crawling with millions of wild, indigenous aerobic bacteria and fungi.
- As soon as the sludge is blended with these materials, it is instantly "re-inoculated" with a fresh, highly active workforce of composting microbes
