Effect of initial pH and pH-adjusted acid on nutrient recovery from hydrolysis urine by combining acidification with evaporation-crystallization

Fertilizer recovery from source-separated urine by evaporation with a combined process of dehumidification and the addition of absorbent resin supplement

Urine is an ideal resource for producing fertilizer, and processes of volume reduction are promising ways to recover nutrients from urine. Because urea is rapidly hydrolyzed in fresh urine, the stabilization of urine is usually necessary to avoid nitrogen loss during evaporation for fertilizer production. In this work, we investigated a new method about rapid evaporation for non-pretreated urine by dehumidification and addition of absorbent resin supplement (ARS). We obtained the optimum operating parameters, they were: 40 °C of temperature, 40 % of humidity, 460 cm2/ (L urine) of area, and 16.7 g ARS/(L urine). ARS absorbed the urine completely and quickly, and the moisture in the system was collected by the dehumidifier to keep the constant dry treatment area. Formation of a high salt content in the treatment area further inhibited the hydrolysis of urea, and finally, urea crystals were harvested. This study achieved a high water evaporation efficiency of 95 % and a high recovery fraction (92.2 % of nitrogen and 100 % of phosphorus) at a low temperature of 40 °C. The crystals included CO(NH)2 and NH4Cl, which are ideal fertilizers for vegetation. The results of this study demonstrated that dehumidification combined with addition of ARS for source-separated urine dehydration is a cost-effective and green technology for urine nutrition recovery.

An integrated strategy for nutrient harvesting from hydrolyzed human urine as high-purity products: Tracking of precipitation transformation and precise regulation

The nutrient recovery from source-separated urine is of great significance for a sustainable and closed nutrient loop. However, common urine-processing techniques have several constraints, including inefficient recovery, low product purity and incapability of simultaneously harvesting multiple nutrients. In this study, an integrated strategy of P precipitation and N stripping was first proposed to harvest nutrients from hydrolyzed human urine as high-purity products via precisely regulating Ca/P dosing ratio. Ca(OH)2 was utilized to trigger Ca-P precipitation and elevate pH level. Different from the previously reported conventional struvite method, P recovery was oriented to calcium phosphate. P harvesting behavior was investigated as a function of key factors including initial P concentration and the dosing ratio. A thermodynamic model was constructed to unveil the precipitation transformation mechanism and visualize P recovery for an enhanced controllability. For N harvesting, Ca(OH)2 was dosed to increase the pH of the urine to converts ammonium to ammonia. The resulting ammonia was stripped and then adsorbed by H2SO4 as high-purity ammonium sulfate. Moreover, the sulfate derived from acidification treatment was recovered as calcium sulfate in the interests of material recycling and mitigating secondary contaminations. Results exhibited P recovery efficiency could reach 100 % and purity for calcium phosphate could be above 90 % within a Ca/P ratio range of 1.67-2.0. Further boosting pH to 12, over 85 % of S and 95 % of N was retrieved. The comprehensive scheme provides an efficient approach towards the precise P and N harvesting from hydrolyzed urine and advances the knowledge of precipitation transformation mechanism.

State of the art of urine treatment technologies: A critical review

Over the last 15 years, urine treatment technologies have developed from lab studies of a few pioneers to an interesting innovation, attracting attention from a growing number of process engineers. In this broad review, we present literature from more than a decade on biological, physical-chemical and electrochemical urine treatment processes. Like in the first review on urine treatment from 2006, we categorize the technologies according to the following objectives: stabilization, volume reduction, targeted N-recovery, targeted P-recovery, nutrient removal, sanitization, and handling of organic micropollutants. We add energy recovery as a new objective, because extensive work has been done on electrochemical energy harvesting, especially with bio-electrochemical systems. Our review reveals that biological processes are a good choice for urine stabilization. They have the advantage of little demand for chemicals and energy. Due to instabilities, however, they are not suited for bathroom applications and they cannot provide the desired volume reduction on their own. A number of physical-chemical treatment technologies are applicable at bathroom scale and can provide the necessary volume reduction, but only with a steady supply of chemicals and often with high demand for energy and maintenance. Electrochemical processes is a recent, but rapidly growing field, which could give rise to exciting technologies at bathroom scale, although energy production might only be interesting for niche applications. The review includes a qualitative assessment of all unit processes. A quantitative comparison of treatment performance was not the goal of the study and could anyway only be done for complete treatment trains. An important next step in urine technology research and development will be the combination of unit processes to set up and test robust treatment trains. We hope that the present review will help guide these efforts to accelerate the development towards a mature technology with pilot scale and eventually full-scale implementations.

Insight into the effect of pH-adjusted acid on thermodynamic properties and crystallization sequence during evaporative-crystallization process of hydrolyzed urine

The evaporative-crystallization process (ECP) is a frequently used approach for complete nutrient recovery from human urine, and crystallization sequence is related to the selection of seed and the optimization of crystallization process. In this study, three hydrolyzed urine (HU) samples, which were acidified to an initial pH of 4 with HCl, H₂SO₄, and H₃PO₄, were used to recover crystallized products by ECP, their crystallization process and thermodynamic properties during ECP were compared, and the detailed crystallization sequence was analyzed using the PHREEQC-2 simulation. The results showed that the pH-adjusted acid has a significant effect on crystal precipitation, and the new crystal in HCl-4-HU, H₂SO₄-4-HU, and H₃PO₄-4-HU first appeared at volume concentration factors (CF_V) of 19.61, 9.90, and 9.96, respectively. Furthermore, the simulated crystallization process characteristics of HU by PHREEQC-2 have a good fit with the actual experimental data, and crystallization sequence of HCl-4-HU, H₂SO₄-4-HU, H₃PO₄-4-HU during ECP were NH₄Cl (CF_V from 10.25 to 100) / NaCl (CF_V from 71.43 to 100), NH₄NaSO₄ (CF_V from 10.25 to 55.56) / NH₄Cl (CF_V from 20 to 100) / (NH₄)₂SO₄ (CF_V from 40.45 to 100), NH₄H₂PO₄ (CF_V from 10.25 to 100) / NaH₂PO₄ (CF_V from38.46 to 55.5) / NaCl (CF_V from 45.46 to 100), respectively. The present study clearly reveals the crystallization sequence and thermodynamic properties of nutrient elements in acidified HU, which provides an important theoretical basis for the optimization of crystallized products obtained from HU for future study.

Separation and purification of α-ketoglutarate and pyruvate from the fermentation broth of Yarrowia lipolytica

A strategy to achieve the efficient co-production of α-ketoglutarate (KGA) and pyruvate (PYR) via Yarrowia lipolytica fermentation was established in our previous work. The next big challenge is to achieve an efficient separation of the two keto acids. A strategy for simultaneously separating and purifying KGA and PYR based on their different boiling points was established, leading to the efficient separation and purification of the two keto acids from the fermentation broth of Y. lipolytica. The purity and yield of KGA/PYR reached 99.3/99.5 and 79.8/80.6%, respectively. Application of the separation method on industrial scale could further decrease the cost of the production of the two keto acids by biotechnological routes.