Importance of Nutrient Recovery from Source Separated Urine
Urine is a source of some important nutrients and by improving the nutrient in it, we reduce some environmental problems. The nutrients can be used to make nitrogenous fertilizers, which increase crop yields. Behind protecting our environment, fertilizer costs are also reduced. Urine that is collected in UDDTs is not the same as the urine collected when fresh. In storage tanks, organic biodegrading substances are broken down by microorganisms.
When treating urine, sanitation is very important to both the person taking the analysis as well as the environment. Each individual excretes almost 2 litres of urine daily, on average. Central waste water treatment plants are known to use conventional concept of sanitation. Other waste water streams are used to dilute urine many times. This dilution effectively removes micro pollutants, such as medicines and hormones. It also helps to boost the valuable components recovery. In the final product, there is a recovery of almost all nutrients.
The only exception is little ammonia that volatilizes in the distillation process and nutrients in the excess withdrawn sludge, which are all negligible. Only 2% of the total nitrogen amount is lost (Udert and Wächter 2012). In the collection tanks, there is precipitation of around 32% of the phosphate. It may as well not reach the nitrification reactor, meaning the tanks used to store urine should be thoroughly cleaned to collect the solids, in an attempt to maximize the recovery of nutrients.
A wastewater treatment plant that is centralized and has a good sewer system represents the best approach to manage wastewater (Cai et al. 2013).This system, however, is limited in some ways. An extensive infrastructural network as well as large water amounts is required. Some decentralized reactors that are highly efficient and small can be used instead. In the management of wastewater, therefore, they create room for more flexibility.
In an attempt to come up with processes that can be used in such treatments of wastewater, Luo et al. (2014) developed some 3 principles: Resource recovery was the first one. The main focus was to recover all the resources that wastewater streams contain, in this treatment. The second principle was decentralization. Proximity to the source is very important. If the source is not far away from waste streams, resource consumption will be minimized. There will also be minimal pollution of environment. Separation at the source was the third principle. There are different compositions in waste streams. They should thus be treated differently in line with their features.
The finite material resources as well as non-renewable energy are used on the current production of fertilizer. All humans excrete nutrients consumed through faeces and urine. They then find their way into wastewater streams. Urine alone carries the most nutrients found in wastewater. These nutrients could become important fertilizer if they are recovered through source-separation. Struvite precipitation is the most reliable process of recovering nutrients to date (Cai et al. 2013). Most of the nitrogen (N) is, however, left in the liquid phase, as only phosphorus (P) is recovered in the process. Microbial Electrochemical Technologies (METs) use the substrate source-separated urine. Because urine has promising properties, the substrate has recently gained interest.
Recovery Processes for Nutrients
Some of the critical global issues affecting the rising population are the freshwater and nutrients shortages. Rizzo et al. (2013) believes that this problem can however be addressed by one promising approach, using the decentralized resource recovery in conjunction with source separation of waste streams. Some 52% of phosphorus (P) and 80% of nitrogen (N) are contained in urine found in a single percent of wastewater in households. Microalgae help in the efficient uptake of nutrients. As a promising technology, they should be grown in urine. Biomass in return is produced as fertilizer in addition to cleaning urine. In their study, Podol et al. (2017) developed an efficient process of recovering nutrients. On porous substrate photo bioreactors (PSBRs), they used immobilized microalgae cultivation. The human urine was minimally diluted. With an exception of a 1:1 dilution with clean water, urine treatment was not amended. The green alga Desmodesmus abundans was used to treat. It was selected between 98 algal strains obtained from culture collections and enrichments specific to activated carbon. It assisted to remove likely pharmaceutical detrimental effects. PSBRs are very effective when combined with other technologies. It could help to close the link between food production and sanitation by using resource recovery systems that are decentralized (Acien et al. 2012).
We can obtain a concentrated urine stream if we apply a concept of source separation, says Udert et al. (2015). As available in wastewater, urine has about 10% of the COD, 50% phosphorus, 70% potassium, and 80% nitrogen. There is also a high concentration of micro-pollutants.
There is more efficient micro-pollutants removal, and energy/nutrients recovery in the concentrated stream. To recover energy and nutrients from human urine, testing and development of technologies is the main aim. Separation, conversion, and collection of various valuable fractions are the major challenges. The fractions are: MgNH4PO4, K+-salts, Ca2+-salts, NH3 and energy. Struvite precipitation is also the recommended method of recovering nutrient in source separated urine (Ronteltap, Maurer, Hausherr, and Gujer, W 2010).
The conventional urban drainage has only one resource-efficient alternative- the source separation and human urine treatment. It recovers important resources from waste streams, in addition to decreasing the wastewater treatment plants’ nutrient load. From real urine, Li et al. (2016) recovered on-site phosphorus in his study. From a reverse process of osmosis, he used brine as the flush water for toilets that divert urine, as well as precipitant P. In a membrane bioreactor (MBR), he used short-cut nitrification-denitrification (SCND) to remove nitrogen (N). By mixing the reverse osmosis brine with urine, he successfully recovered 90% of P under the pH scale of 9.1. 10-16% of P was contained in the recovered precipitates. It can be used in producing phosphate fertilizer.
The MBR saw the achievement of stable SCND. As the denitrification electron donor, during the removal of organic compounds in urine, 45% of N was released. Denitrification was significantly elevated by adding methanol. This in return refilled the alkalinity needed for nitrification. In the combined MBR process and precipitation, there was removal of more than 90% of N, 90% of organics, and 99% of P. The predominant ammonium oxidizing bacteria was nitrosomonas. As shown by fluorescence in pyro sequencing technique and situ hybridization, the nitrite oxidising bacteria were not present in the microbial communities. The prevailing factors that inhibit NOB growth are low dissolved oxygen, and high nitrite acids and free ammonia concentrations. In the MBR, the high concentration facilitated the stable SCND operation.
Challenges Associated with Collection, Conversion, and Separation of Valuable Fractions
According to Udert and Wächter (2012) freshly released urine contains degraded soluble organic compounds, salts and hydrolysed urea. When hydrolysis occurs, ammonia is released and this leads to rise in PH up to 9.2. The subsequent solution is more unstable and the substances are precipitated out, although they contain low solubility. Correct stabilisation of urine hinders the breakdown of organic matter which in turn produces foul smell, precipitation activity, and volatilisation of ammonia (Coppens et al. 2010). This activity is controlled by microbial processes; it means to prevent the growth of microorganism which is crucial process.
Nitrification is a biological process which is more sensitive than even chemical process. Here there is a very serious nitrite build-up. When there is a small change in the inflow of rate or in the reactor, it can then destabilise the complex balance between nitrite oxidising bacteria and ammonia. This is done to help the nitrile accumulate. The concentration above 50mgN needs a midway to prevent more accumulation. And prevention of nitrifying bacteria has shown that if the inflow rate is increased by about 10%, it may lead to tragic accumulation of nitrile. Detection of nitrile is the main feature of stabilised urine nitrification reactor.
Acidification has been used in detail for urine stabilisation, which is achieved by use of ultrafiltration and microfiltration (Udert and Wächter 2012). Evidence is available from research material of unrease inhibitors to prevent hydrolysis of urine. Acidification is a method of preventing hydrolysis of urea and to keep the PH in the storage tank below 4 to for more than 250 days and to prevent urea hydrolysis.
The experiment carried out shows that 60 mmmoIHp 11 urine of a strong acid makes the PH below 4 for more days about 250 and above. Acidification has some side effects which are positive with regard to hygiene due to crucial effect of pathogens at a pH below 4. Reduced PH ranges have an effect on therapeutics found in urine (Udert and Wächter 2012). At pH 2 there is activation level that is between 50 -95%. This may be found for antibiotics and some anti-flammatory drugs.
Partial nitrification is also a good method that lowers the PH, but there is no other compatible buffer which is found in urine at certain concentration. Nitrification of urine can only oxidise about half of the ammonia available until nitrification stops due to low pH levels. When the level of nitrite is considerably high it, has an effect on nitrile oxidisers since their sensitivity is affected by nitrous oxide. Ammonia is completely converted and this affects the nitrile and thus inhibited. The experiment done by Kumar, Hart and McCalley (2011) shows that the outcome of nitrification of urine is either one of the two; ammonia nitrite or ammonia nitrate solution, with a ratio of 1:1 composition makeup.
According to Randall et al.(2016), the stabilization of fresh urine with calcium (Ca(OH)2 ) is another method. They conducted some investigation of long term effects of urine treated with Ca(OH)2, where 1l of fresh urine is added to Ca(OH)2. There is addition of urease to the groups so as to get 3000gNm-3d-1 rate of urea hydrolysis. Two control experiments can be carried out, where one is added, neither Ca(OH)2 nor urease and the other with urease without Ca(OH)2 to ( Randall et al.2016). They are then covered so as to decrease volatilization of ammonia and stirred continuously.
Urine Stabilization Techniques
Ammonia pH and concentration are measured regularly. Stabilization takes 27 days. When Ca (OH) 2 is added, urea hydrolysis is prevented (Elliott 2013). Where there is urine without Ca (OH) 2 and urease, and the ammonia is increasing slowly, this doubles ammonium concentration, thus indicating a few urease active microorganism in urine. The ammonia concentration increases rapidly after untreated urine is spiked with urease while that spiked with calcium hydroxide it remains the same. This indicates that the PH rapidly increases to 9.9. When urine is spiked with urease, pure urine slowly increases to 7.7. When spiked in a solution of sodium hydroxide with, the PH is raised to 12.4. This indicates that the less the PH values, the more ammonia is produced. It has been shown that urea hydrolysis depends on PH.
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