Composting And Food Waste Biology Essay


Food waste has been a large job all over the universe. Harmonizing to Hong Kong Environmental Protection Department ( HKEPD, 2008 ) , approximately 9,300 metric tons of municipal solid waste ( MSW ) was disposed at landfills everyday. The organic fraction of the MSW was chiefly nutrient waste and pace waste, which amounts to over 3,600 metric tons, representing about 38 % and is the largest fraction of the MSW. The disposal of such biodegradable waste direct to the landfills causes a job in Hong Kong as it leads to rapid depletion of the limited landfill null infinite and the formation of landfill gas and leachate that impose long term environmental load on our environment.

Hong Kong authorities has started turn toing the job of nutrient waste by suggesting some biological interventions such as composting and anaerobiotic digestion since 2005. Food waste undergoes a natural decomposition by the bugs during composting. It turns the organic substrate into a stabilised organic signifier which can move as foods to the workss.

phosphate ( MAP, MgNH4PO4 i?Z6H2O ) as described in the undermentioned equation:

Mg2+ + PO4 + NH4+ + 6H2O = MgNH4PO4i?Z6H2O ( Nelson et al, 2003 )

The formation of struvite helps to retain a high fraction of N content in the compost and organize a high value fertiliser as it is a slow releasing fertiliser supplying N, P and K to the workss. ( Ren et al.,2010 ) had found that the molar ratio of Mg to PO4 peers to 1 to 2 was suited for the struvite formation ; hence Mg to PO4 as 0.05 M to 0.1 M was used in this experiment. Furthermore, 0.05M MgO was used since some research show that the concentration of MgO higher than 0.05M inhibited organic affair decomposition during composting. ( Lee et al,2009 ) Further, to keep the typical struvite formation ration, a intervention incorporating Mg to PO4 as 0.05 M to 0.05M was besides used for comparing.

formation is 8-9 ( Lee et al. , 2009 ) . Therefore, add-on of calcium hydroxide was considered to relieve the low pH status every bit good as to advance the struvite formation

Research Objective and Outlines

The aim of this experiment is to measure the consequence of calcium hydroxide, MgO and K2HPO4 add-on in different concentrations in nutrient waste composting by comparing ( I ) the decomposition public presentation, ( two ) the alimentary value, ( two ) the struvite formation and ( three ) adulthood clip of compost.

Chapter 2 Literature Review

2.1 Definition of composting

Composting is a natural decomposition procedure that the organic substrate degraded by the micro-organism into a stabilised organic substance under an aerophilic status. ( Haug, 1993 ) It is an environmental friendly and cost effectual method to repair the waste job. As the some phytotoxic substance can be degraded together with the organic affair and the full-blown compost can be used as fertiliser. ( de Bertoldi et Al, 1983 )

However, the alimentary value in the compost will be greatly reduced from the loss of N in signifier of ammonium hydroxide during the composting procedure. The ammonium hydroxide emitted will besides take to a olfactory property job. It is really of import to cut down the sum of ammonia emanation and hence work outing the serious olfactory property job and bring forthing high quality fertiliser.

2.2 Factor impacting decomposition procedure

2.2.1 Microbial activity

There are many different micro-organisms in the compost mass during the composting procedure. They are responsible for different portion in the debasement of organic affair. Bacteria, Fungi

and besides actinomycetes take a of import function during the composting.

Bacteria is the most important in debasement of compost. There are different species of bacteriums dominate in different phrase during composting. For illustration, Staphylococci dominate in mesophilic growing stage ( Hassen et al,2001 ) ; Bacillus and Clostridium dominate in thermophilic stage. ( Strom, 1985b )

At the ulterior phase, the temperature of the compost lessening which facilitate the growing of actinomycetes. ( Miller, 1996 ) For illustration, the Streptomycess and Thermomonospora dominate in ulterior phase of composting.

Fungi and besides actinomycetes will utilize up the saccharide remained such as lignin, cellulose and besides hemicelluloses. ( Miller, 1991 )

2.2.2 Foods ( C/N ratio )

Alimentary influences the microbic growing. Carbon and N are the foods which are most of import for the micro-organism in the compost. Carbon supports the cellular growing of the micro-organism while the N can back up the protein synthesis of micro-organism. The best C/N ratio for the growing of bugs is 30:1 ( Epstein, 1997 ) The composting procedure will be hindered by the incorrect initial C/N ratio. If the C/N ratio is every bit low as 15, which spend much more clip to be mature than that of the waste with C/N ratio 30. Besides slow debasement rate, the low C/N ratio will besides advance the N volatilization to let go of ammonium hydroxide gas which resulted in a low quality fertiliser. ( Epstein, 1997 ) When C/N ratio is

2.2.3 Moisture content

Water is indispensable for all micro-organisms during composting as H2O can back up their life and besides mobility to derive nutrient from the surface of the waste. ( Rynk, 2000 ) The ideal wet content for composting would be 50-60 % ( Rynk, 2000 ) that which can be adjusted by adding H2O or sawdust. If the wet content is higher than 60 % , an anaerobiotic status is resulted which suppress incoming O ( Seekins, 1999 ) by the H2O as the porousness of compost stuff is reduced with the high compression. ( Das and Keener, 1997 ) However, if the wet content lower than 40 % , the microbic activity will cut down as the microbic metamorphosis is hindered which resulted in a immature compost.

2.2.4 Temperature

Temperature affects the community and besides activity of the micro-organism and hence impacting the debasement of the compost. Sanitation can be achieved in the high temperature which can take the pathogen in the compost and let the compost be mature. ( Epstein, 1997 ) However, the high temperature excced 80a„? ceases the microbic activity and greatly cut down the decomposition rate of the compost.

2.2.5 pH

The decomposition rate of compost is extremely controlled by pH. When the pH is 6 or below, the initial decomposition is reduced ( Nakasaki et al, 1993 ) as the alkalic status favor the microbic activity and community. When under low pH, the volatile fatty acid is promoted ( Brinto,1998 ) while ammonium hydroxide gas is promoted under high pH owing to the ammonium volatilization. ( Gage, 2003 ) However, the quality of compost is lowered by increasing loss of N.

2.3 Factor impacting nitrogen loss

During composting, the organic N transmutation by the micro-organism will bring forth ammonium hydroxide as by-product. The ammonium hydroxide can be in signifier of volatile gas or retain in the compost. Presence of ammonium hydroxide is of import as it can increase the pH in compost in order to heighten the debasement of organic affair. ( Jeong and Hwang, 2005 ) The retained ammonium hydroxide will converted to a nitrate by nitrifying bacteriums, particularly at the maturating phase during the composting ( less than 40a„? ) ( Sanchez-Monedero et al. , 2001 ) There are some factors impacting the ammonia emanation rate. First, the low C/N ratio will let go of more ammonia gas as there are less organic affair to back up the growing of the micro-organism which in bend lower the nitrogen assimilation by bugs and therefore increasing the keeping clip of N staying in compost. For illustration, the loss of N can up to 43-62 % of original N, depending on the amendment added. ( Eklind and Kirchman, 2000 ) Other survey besides shown that the loss of N in high N incorporating municipal solid waste can amount up to 40 % . ( Sanchez_ Mondedero et Al, 2001 ) Second, the temperature will besides increase the ammonia volatilization rate as ammonium hydroxide will be more easy to be converted into gaseous signifier under high temperature. Third the aeration rate besides affects the nitrogen loss in gaseous signifier as the higher the aeration rate the more the ammonium hydroxide gas carried off to air outside the composter. Besides, the commixture and turning of compost will besides account for the higher ammonia volatilization rate. ( Morisaki et al, 1989 )

The N may besides loss in signifier of nitrogen oxide in gaseous signifier which can amount up to 20 % of initial N. ( Bernal et Al, 1993 )

2.4 Struvite formation

2.4.1 Optimum formation status

Struvite is a crystal called Mg ammonium phosphate which formed by Mg, ammonium and phosphate in a ratio of 1:1:1 in the undermentioned equation.

Mg2+ + PO4 + NH4+ + 6H2O = MgNH4PO4i?Z6H2O ( Nelson et al, 2003 )

pH value, temperature, other sorts of ion, solubility of struvite and the grade of supersaturation.are crucial for the struvite precipitation. ( James and Simon, 2002 ) . Struvite can organize from pH 7 to 11 while the optimal pH for struvite formation would be 8.5 to 9.2 in effluent. ( Uludag-Demirer et Al, 2005 )

2.4.2 Advantage of struvite formation in compost

As ammonium ions are captured by the Mg and phosphate ions for the formation of struvite, the N content in the compost can be conserved and therefore less odor job resulted as less ammonium hydroxide gas emitted. ( Jeong and Kim, 2001 ) The maximal recovery of ammonium- N can make 92 % in landfill leachate ( Uludag-Demirer et al,2005 ) while it can make up to 95 % under aerophilic digestion. ( Ganrot et al, 2007 ) Struvite is slow let go ofing fertilisers which merely somewhat soluble in impersonal or alkalic status while it is readily soluble in acidic status. ( D.G.Chirmuley, 1994 ) Furthermore, it is non easy flashed away by rain H2O. Therefore, it would be more effectual when using on sloppy and acidic country. ( L.Pastor et Al, 2008 )

Chapter 3 Methodology

3.1 Composting control system

There was a computing machine commanding five 20L chromium steel steel containers where the composting procedure carried out indoors. There was a metal palpebra and a plastic “ O ” pealing covering the composter which was screwed tightly by eight prison guards in order to forestall the escape of gas from the composter.

A bed of heat insulating froth was injected environing the composter in order to cut down the heat loss during composting. The construction of composter were as shown in Figure 3.1.

Figure 3.1 Diagram of insulating construction of a composter

3.2 Preparation of nutrient waste mix

Food waste were made from staff of life, veggie, rice and boiled porc in ratio of 13:10:10:5 unnaturally. All the nutrient waste was cut into 1 cm3 for homogeneous commixture. The C/N ratio was adjusted by adding 9100 g oven-dried sawdust. For each armored combat vehicle, approximately 7.0 kilograms of the mix were added, and so the calcium hydroxide, Magnesium oxide and dipotassium H phosphate were added in different concentrations. 500 g plastic beans was added to each armored combat vehicle to accomplish a majority denseness of about 0.5kg/L. The wet content were adjusted into a 55 % by adding 1.5L dionized H2O. The aeration was set in 0.5 Fifty min-1 kg-1 DW for the first hebdomad and so put to 0.25 L min-1 kg-1 DW afterwards.

3.3 Treatment and experimental design

There are five interventions in my experiment, R1 is the control without any add-on. R2 with calcium hydroxide added merely as lime provide a alkalic status prefering the composting procedure. For R3 and R4, both with the add-on of calcium hydroxide, Mg oxide and dipotassium H phosphate. However, Magnesium ion to phosphate ion ratio was 1:1 in R3 while it is 1:2in R4. These two interventions were set to compare the better ratio for the struvite formation during composting. Besides, R4 and R5 had the same concentration of Magnesium and phosphate but there was no lime add-on in R5 which is set to look into whether calcium hydroxide favor the formation of struvite.

Table 3.1 Experimental designs of different interventions in nutrient waste composting



Calcium hydroxide

( g per Tank )


( g per Tank )


( g per Tank )


Control ( without add-on of calcium hydroxide, MgO and K2HPO4 )





Addition of 2.25 % calcium hydroxide,





Addition of 2.25 % calcium hydroxide, 0.05M MgO and 0.1M K2HPO4 ( Mg: P = 1:2 )





Addition of 2.25 % calcium hydroxide, 0.05M MgO and 0.05M K2HPO ( Mg: P = 1:1 )





Addition of 0.05M MgO and 0.1M K2HPO ( Mg: P = 1:2 )




3.4 Gas injection and aggregation

The undermentioned Figure 3.2 shows the experimental apparatus of the composter. Air was flowed from the aeration pump and passed into the composter. The gas emitted was released into a fume goon in normal status.

When mensurating the ammonium hydroxide gas emanation, the outflow of gas was collected to a iced H2O capacitor and so a conelike flask incorporating the 100ml 0.4M boracic acid to pin down the ammonium hydroxide for an hr.

When mensurating C dioxide development, the surpassing air was collected to a wet trap to take the wet in the gas and step the C dioxide development by the C dioxide analyser.

Figure 3.2 Diagram of experimental apparatus

3.5 Compost sampling

There are eight trying yearss in my experiment, they were twenty-four hours 0, 3, 7, 14, 21, 28, 42 and 56. In each sampling twenty-four hours, the nutrient waste from five composters were assorted in different armored combat vehicles. The mixing yearss were twenty-four hours 0, 3, 7, 10, 14, 17, 21, 28, 35, 42 and 56. During blending the compost, H2O was added by expression and experience method to keep the H2O wet of compost to around 60 % . ( Rynk, 2000 ) 100g of extra samples were obtained from each composter.

3.6 Gas analysis

3.6.1 Carbon dioxide

The surpassing gas was collected to a wet trap which composed of silicon oxide gel and so clonnected to a C dioxide analyser ( WMA-3, P P System, UK ) . The reading of C dioxide were obtained.

3.6.2 Ammonia

Ammonia was trapped by a conelike flask incorporating 0.4M boracic acerb solution with bromocresel green- methyl ruddy index. The ammonium hydroxide trap was replaced every twenty-four hours. The solution obtained after linking to the surpassing gas of composter was titrated against 0.1M HCl to give a blood ruddy terminal point.

3.7 Compost quality analysis

There were 10 parametric quantities carried out in the experiment to find the compost quality of nutrient waste. They were pH, EC, wet content, extractible ammonium, entire N, nitrate and nitrite, entire P, entire organic C, entire organic affair and seed sprouting index. For fixing the H2O infusion, 20g fresh compost sample was shaken with DI H2O at a ratio of 1:5 dry weight per volume for one hr and kept it still for half an hr. pH was measured by Orion 920A ISE ionanalyser and EC was measured by Orion 160 conduction metre after the H2O extraction of compost. The suspension in the H2O extraction was removed by the centrifugation at 13500 revolutions per minute for 20 proceedingss earlier filtered out by go throughing through 0.45Aµm membrane filter. The filtrate was used for seed sprouting trial, indophenols-blue method, Cadmium decrease method for the analysis of adulthood of compost, extractible ammonium and besides nitrate severally.

The wet content are measured by hydrometric method that the fresh compost was weighted and put into 105a„? oven for 48 hour ( Rynk, 2000 ) The oven dried samples were so being put into a 550a„? oven for 16 hours to mensurate the TOM. While TOC was determined by the Walkey- Black method by utilizing air dried samples which were put in the 55a„? oven for 24 hour. The air dried samples were used for indophenol blue and vandomolybdphosphoric acid method after acerb digestion for entire N and entire P finding severally.

3.8 Precipitate analysis

The dried samples were grinded and analyzed by X-ray diffraction through a X beam diffractrometer. ( XRD, Bruker D8 Advance Xray Diffractrometer ) The pulverization XRD form of interventions were compared with the XRD form of standard struvite by fiting the place and besides the strength of extremum of the crystal construction.

Chapter 4 Result and treatment

4.1 Change of temperature

Temperature affects the activity and population of micro-organism which in bend affects the rate of decomposition. Besides, it achieves sanitation if the temperature remains higher than 55 a„? to 60a„? for three twenty-four hours, it can kill the pathogen in the compost and turn it to be mature. ( Stentiford, 1996 )

In Figure 4.1, all the interventions raised to a high temperature at the beginning. However, R1 ( unreal nutrient waste without any add-on ) and R4 ( Addition of 2.25 % calcium hydroxide, 0.05M MgO and 0.1M K2HPO4 ) could non keep a high temperature for a period of clip and dropped back to room temperature rapidly which were caused by the acerb suppression and therefore less heat released. For other interventions, both were able to keep a high temperature for at least one hebdomad which indicated that they underwent a normal composting procedure.

Fiugure 4.1 Change of temperature during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.2 Change of pH

The initial pH varied because of different lime add-on. There was a general diminishing tendency in the first few yearss. There were two grounds for the lessening of pH. It might diminish because of the microbic change overing the ammonium ion into microbic biomass aerobically. ( Beck-Fiss et al,2003 ) Besides, it may besides dropped due to the organic acid formed during the decomposition of organic affair. ( Nakasaki et al,1993 )

In Figure 4.2, the pH of control dropped at the beginning and kept at a low pH afterwards. While R4 ( Addition of 2.25 % calcium hydroxide, 0.05M MgO and 0.1M K2HPO4 ) dropped into a low pH for a period and so raised to a higher pH later. While the other interventions maintained in a higher pH which favored the composting procedure which indicated the add-on of calcium hydroxide can buffering the organic acid formation under a low pH. ( Nakasaki et al,1993 )

Figure 4.2 Changes of pH during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.3 Changes of C content in compost

4.3.1 Carbon dioxide development

The C was chiefly lost in from of C dioxide as C dioxide released during the decomposition of saccharides. ( Baca et al, 1993 ) The C dioxide addition proportional to the microbic activity.

In Figure 4.3, all the interventions increase dramatically at the beginning and so diminish subsequently. Control and R4 decrease rapidly less than a hebdomad due to the acerb suppression. While the other interventions maintained a high CO2 development for a hebdomad which indicated a high microbic activity and therefore a normal composting procedure. The development are bit by bit decrease due to the available food are readily depleted for the micro-organism.

From Figure 4.4, R2, R3, and R5 has a higher than two-base hit of cumulative CO2 development to that of control and R4. The low CO2 development in R1 and R4 are chiefly caused by the low pH which inhibit the microbic activity and hence lower the decomposition of organic affair.

Figure 4.3 Daily C dioxide developments during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

Figure 4.4 Accumulative C dioxide development during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.3.2 Changes of entire organic affair

The decrease of entire organic affair is used to bespeak the decomposition rate as the organic affair is degraded. ( Epstein, 1997 ) The alterations of entire organic affair should be correlated with the CO2 development. From Figure 4.5, the R2, R3 and R5 had a big decrease of TOM, which besides had a high CO2 development.

While the control and R4 had a smaller decrease of TOM which correlated with the low CO2 development. The slow decrease of CO2 development was caused by the acerb suppression on the microbic activity and therefore less organic affair was decomposed.

Figure 4.5 Changes of entire organic C during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.3.3 Changes of entire organic C

Entire organic C is besides an index for the debasement rate. It besides decreased against the CO2 development due to the mineralization if C in nutrient wastes to the C dioxide.

As Figure 4.6 shows, TOC cut down with the composting yearss. Control and R4 about had no alteration on the TOC decrease due to the low pH impeding the microbic activity and resulted in a low debasement rate. After 56 yearss, 0.64 % , 14.18 % , 2.54 % , 18.47 % and 20.90 % of entire organic C were degraded in R1, R2, R3, R4 and R5 severally. The debasement rate is the highest in R5 which besides had the highest CO2 development. The TOC content in other interventions besides correlated to the CO2 development.

Figure 4.6 Changes of entire organic C during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.4 Changes of N content in compost

4.4.1 Changes of soluble ammonium

From Figure 4.7, It increased at the beginning in all intervention due to the ammonification carried out by the micro-organism. There are three grounds account for the lessening of ammonium afterward. First, it removed in signifier of ammonium hydroxide. Second, it was taken up by the micro-organism for growing which could be represented by equation 1 Third, it converted to nitrate by microbic activity which could be represented by equation 2.

NH4+ + 2O2 i? NO3- + 2H+ + H2O — — — — — — — — — — — — — -Equation 1 ( Polprasert,1989 )

NH4+ + 4CO2 + HCO3- + H2O i? C5H7O2N + 5O2 — — — -Equation 2 ( Polprasert,1989 )

R1 and R4 gave a really low sum of extractible ammonium as the microbic activity was inhibited by the low pH and therefore hindered the ammonification which carried out by micro-organism.

R2 and R3also had a high sum of extractible ammonium as calcium hydroxide is added which produced a alkalic status to advance the growing of micro-organism and besides to ease the ammonification. ( Jeong and Hwang, 2005 )

While R5 produced less ammonium than R2 and R3 as there was no lime add-on to supply a alkalic status to heighten the ammonification. Besides, the formation of struvite captured the ammonium ion which besides lower the sum of soluble ammonium in R5.

Figure 4.7 The alterations of extractible ammonium during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.4.2 Ammonia emanation

During the debasement of protein in the nutrient waste, ammonium hydroxide would be released under a high pH status. ( Nakasaki et al, 1993 ) Volatilization of N incorporating compound lead to the formation of ammonium hydroxide gas under a alkalic status. ( Jeong and Hwang, 2005 ) Its chiefly caused by the displacement of equilibrium under high pH value by the action of micro-organism and as shown in the undermentioned equation.

2A NH3A ( cubic decimeter ) A A NH4A ( aq ) +A NH2A ( aq ) — — — — — — — — — — — Equation3

From Figure 4.8, there was a crisp addition of ammonia emanation for first two hebdomads form all interventions except control and R4. Control and R4 merely had a little sum of ammonium hydroxide released as their debasement rate is excessively low to bring forth high concentration of ammonium hydroxide and their pH value is excessively low to switch the equilibrium to breathe ammonium hydroxide gas.

While R2 had the highest emanation because of its high pH value. For R3 and R5, the ammonium hydroxide released is much less than that of intervention 2 as the there were precipitates formed which capturing the ammonium ions and hence cut down the ammonium hydroxide loss.

Figure 4.8 Changes of day-to-day ammonium gas emanation during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

Figure 4.9 Changes of cumulative ammonium gas emanation during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.4.3 Changes of entire N

As there was a lost in compost mass owing to the decomposition of organic affair, the entire N of all interventions are by and large increased. ( Wong et Al, 2009 )

From Figure 4.10, control and R4 merely had a little addition in entire N which indicates a slow decomposition rate with little loss of dry weight. While for the R2, R3 and R5, the entire N is little or less the same. However, as the debasement rate of R5 is highest, the compost mass would be lower and hence a higher concentration of entire nitrogen concentration was given. The entire N of other intervention besides corresponded to the debasement rate.

Figure 4.10 Changes of entire N during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.4.4 Changes of nitrite and nitrate

Nitrate is the terminate signifier of N ( Wong et al, 2009 ) that the ammonium hydroxide was converted to nitrate by the transition of nitrifying bacteriums under an optimal pH 7 to 8. ( USEPA, 2002 )

Form Figure 4.11 and Figure 4.12, R5 had the highest sum of nitrate and nitrite as it had the highest sum of ammonium retained in the ulterior phase of composting. As nitrate is the concluding sink of N, a bead in the nitrite resulted in a rise in nitrate which could shown in R2 and R4.

Figure 4.11 Changes of nitrite during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

Figure 4.12 Changes of nitrate during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.4.5 Change of solid C/N ratio

There was a diminishing tendency on the C/N ratio as C is lost in signifier of C dioxide bit by bit during the mineralization of organic affair throughout the composting procedure. While the loss of compost mass during the decomposition of nutrient waste accounted for the addition of entire N. As a consequence, there was a decreasing tendency for all the interventions as Figure 4.13 shown.

R1 and R4 had smaller decrease in C/N ratio as the low pH inhibit the biodegradation of organic affair and therefore non a big decrease of C content and big addition in nitrogen content resulted.While the biodegradation of R2, R3 and R5 is fast and therefore resulted in a big decrease of C/N ratio.

C/N ratio could besides bespeak the adulthood of compost that the value smaller than 20 was identified as mature. ( Hirai et al,1983 ) Therefore, R2, R3 and R5 were matured as their C/N ratios were under 20.

Figure 4.14 Changes od C/N ratio during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.5 Crystal formation in compost

Figure 4.15 shows the pulverization X beam diffraction form. There were three crisp extremums in 16,21 and 31 two theta grade. As struvite was a cystal which has a typical orthorhombic construction and so it was easy identified by the X-ray diffraction form. ( Du Xian-yuan et Al, 2010 ) By comparing the pulverization X beam diffraction form of different interventions to the criterion as shown in the Figure 4.16, merely R5 had the pure struvite formed as the extremum of pulverization XRD form in R5 can suit the pulverization XRD form of sruvite criterion.

While there might be some impure crystal formed in other interventions that the extremum of other crystal may shadow the extremum of struvite in XRD patterm and hence it is hard to find the type of crystal signifier.

Figure 4.15 Powder X – beam diffraction form of standard struvite

Figure 4.16 Powder X- beam diffraction form of different interventions

4.6 Entire P

The initial entire P of different interventions was non the same there were different concentrations of dipotassium H phosphate added. For R1 and R2, there was no add-on of dipotassium H phosphate, as a consequence, it had a low initial sum P concentrations. While both R3, R4, R5 besides had the dipotassium H phosphate add-on and hence had a higher initial P concentration. However, R4 and R5 had a higher entire P concentration than that in the R3 as dual concentration ( 0.1M ) of dipotassium H phosphate is added in R4 and R5.

There was an increasing tendency for the entire P as the dry weight of compost decreased along with the biodegradation of nutrient waste. As the P are non volatile, it retained in the compost. Therefore, the higher the decomposition rate the larger the addition of entire P due to the concentration consequence. As a consequence, R5 had a higher TP than R4 even though the same sum of dipotassium H phosphate was added since the decomposition of R5 is the highest among five interventions.

Figure 4.17 Changes of entire P during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.7 Phytotoxicity

4.7.1 Electrical conduction

Electrical conduction reflects the salt in compost which was able to bespeak the phyto repressive consequence on the growing of workss. ( Ren et al, 2010 ) 3.00 mScm-1 was identified as the restricting EC for turning works safely. ( Garcia, 1991 )

Form Figure 4, all the workss had the EC higher than 3 mScm-1. R4 and R5 had higher EC as larger sum of salt was added in this two interventions. While R1, R2 and R3 had a relatively lower EC, as they would non present a serious inhibitory consequence to the works.

Figure 4.18 Changes of electrical conduction during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

4.7.2 Seed sprouting index

Seed sprouting is another adulthood index. Harmonizing to Tiquia and Tam ( 1998a ) , the phytotoxicity is minimum when the sprouting index exceeded 80 % .

From Figure 4.18, both GI in R2, R3and R5 exceeded 80 % and hence they were uitable for the works to growing. However, even the GI in R5 was higher than 80 % but it was much lower than that of R2and R3 because of its high electrical conduction which posed a phyto inhibitory consequence on works growing.

While R1 and R4 showed a really low GI due to a low pH which inhibit the microbic activity and hence giving a slow debasement of organic affair suppressing the works growing.

Figure 4.19 Changes of sprouting index during the nutrient waste composting with different concentration of calcium hydroxide, Magnesium oxide and dipotassium H phosphate.

Chapter 5 Decision and farther surveies

5.1 Decision

The pure struvite merely signifier in R5 ( Addition of 0.05M MgO and 0.1M K2HPO4 ) has no lime add-on, which mean there are interaction between the calcium hydroxide and phosphate which hinders the formation of struvite. Besides, although the struvite signifier in R5, the sum of nitrogen loss is still higher than that of R3 ( Addition of 2.25 % calcium hydroxide, 0.05M MgO and 0.05M K2HPO4 ) . Struvite may non be the best crystal to minimise the nitrogen loss during the nutrient waste composting.

In term of biodegradation, loss of N and adulthood of compost, R3 is the animal among five interventions as it has the just public presentation on different facets.

5.2 Further Surveies

Although the optimal pH for struvite formation is 8.5-9.2, but the lime add-on can non heighten the struvite formation and may organize other crystal alternatively of. Further probe is need to happen out the interaction between calcium hydroxide and struvite.

Besides, there are other crystals formed in different interventions such as the crystal formed in R3 which can successfully cut down the loss of ammonium hydroxide. As a consequence, a farther surveies could be conducted to place the crystal formed in different interventions and look into the crystal which best minimise the nitrogen loss.