International Journal of Waste Resources

Study of the Physical and Chemical Properties of the Compost Produced from Sawani Composting Plant

Salah A Belkher^* Department of Soil and Water, Faculty of Agriculture, University of Tripoli, Tripoli, Libya
^*Correspondence: Salah A Belkher, Department of Soil and Water, Faculty of Agriculture, University of Tripoli, Tripoli, Libya, Tel: 0917163642, Email:

Received: 09-Jun-2020 Published: 28-Jun-2020, DOI: 10.35248/2252-5211.20.10.383

Introduction

The process of producing compost from municipal solid waste is considered as one of the most important environmental measures applied by many countries for the safe disposal of such waste.

The composting process (controlled biological process under special conditions) must be carried out according to specific technical and environmental requirements to reduce its negative impacts and also to ensure that there are no pollutants in the final product.

The recycling of source separated organic waste results in high quality composts, which could use as an organic fertilizer and as carbon sink [1] The best option is to recycle the components of the municipal solid waste to the maximum as possible, especially the biodegradable organic portion through the composting.

The quality of this final product depends on many of the properties associated with the raw materials involved in the process which have different physical and chemical properties, the origin of this material and other properties relevent to the method of decomposition are; the quality, the conditions under which the process was carried out, humidity, heat, ventilation, carbon to nitrogen ratio, and the practical size.

In addition to the degree of decomposition of the organic matter is the content of nutrients, heavy metals, plant toxic compounds and other properties must be highly considered.

The process of producing and using compost has become an important issue that needs further discussion in some countries of the world, especially in the absence of control measures and legislation that will lead to the success of the production process and stop at the acceptable limits of the environment and health, as well as the requirements of the local market determined by the quality of this product.

The concept of establishing specifications for the compost produced from municipal solid waste and developing quality standards can help in the creating new markets and solve a significant environmental problem.

The concept of compost quality and compost tests produced from municipal solid waste was not known in most countries of the world until the end of 1985.

Warman, et al. [2] studied the effect of compost produced from municipal solid waste on quality characteristics, but they did not find any differences in the amount of vitamins between traditional fertilizing and using compost produced from municipal solid waste for carrots and cabbage.

It was also mentioned [3] that, the heavy metals can be found in the form of salts (carbonates, sulfides, etc.) linked to the organic matter and can be adsorped or exchanged.

In the year 1990 [4] published in his doctoral thesis which was entitled “Quality of Compost from Differing Source Materials “in which he confirmed the possibility of producing compost from municipal solid waste with low in its content of pollutants In 1982, 1990 [5] surveys of heavy presses in household waste were conducted in Germany. These studies promoted environmental interest in the risks of re-use of biodegradable household waste.

Based on the above and an attempt to keep pace with the scientific studies conducted in the world in this field, the thinking was to study the quality of the compost produced from the municipal solid waste in Sawani plant, which is considered as one of the largest compost production plants in Libya. Moreover, it receives large quantities of mixed and multi-source waste that being collected from the city of Tripoli.

Therefore, it was necessary to determine the nature of the produced compost to recognize its properties, characteristics, and its conformity with the specifications and standards adopted in some countries, and the possibility of the improvement in the future.

Specifically, this study aims to determine the quality of the compost produced and to identify its physical and chemical properties and the levels of physical, chemical contaminants and their concentrations , and how much it contains from the nutrients necessary for the plants growth of different agricultural crops as well as identifying the concentrations of heavy metals, and thus trying to be able to determine some of the essential requirements of the quality insurance of the production process or directly related to the final product, taking into consideration the different scientific views, which are due to the methods of tests that are conducted on the compost produced from municipal solid waste.

Materials and Methods

Sampling and preparation

Three Compost samples from the final product which fell from sieve holes were taken three times a day (morning - afternoon - evening) from Sawani plant all over one-year period (starting April 2004).

The apparent density and moisture content of each sample were estimated separately, then those three samples were mixed with each other homogeneously to make one compound sample and then divided the sample into three main parts (Figure 1).

Figure 1: Sampling Method.

As for the other three parts, each of them was divided into two parts, so that the first part for the physical tests, called (the physical sample), was air dried at room temperature over a period ranging from 3-7 days, 100 grams was weighed and used to determine the percentage of foreign matters while the other part is sieved by a set of sieves with different diameters to estimate the particle size distribution of the compost. The compost with particle size of less than 4 mm placed in plastic bags, tightly closed and wrote numbers and symbols indicating the sample collecting date then transferred to Laboratory to performing the Physical tests.

The chemical part was air dried at room temperature over a period ranging from 3 to 7 days. Then it passed through a set of sieves with different diameters. The particles with sizes less than 4 mm, were collected and placed in plastic bags and transferred to a laboratory for chemical analyses.

Analysis

To carry out this study, some important physical, and chemical properties were identified that can be used routinely to assess the quality of the compost produced from municipal solid waste, including:

First, estimate the physical properties:

The degree of maturity: An estimate of this characteristic has been developed by distinguishing the unpleasant odors from the samples, since the emission of such smells is evidence of the presence of organic acids and alcohols and the release of other gases associated with the treatment method and the conditions under which compost was produced.

To confirm the degree of maturity of these samples, other samples were brought from the same compost, but in an advanced stage of decomposition, and compared with it, in terms of smell, color, and particle size. The smell of fresh compost (incomplete decomposition) was very unpleasant, similar to the smell of rotting (fermented) substances. When taking 1 gram and put it in a 100 ml beaker, shake it well and leave it for 2-3 days. The smell is similar to the smell of wastewater. The particles were large, while the comparison sample has a smell of forest soil, dark brown color with fine particle size.

The presence of foreign matters: The percentage of glass and plastic as foreign matters were estimated by taking a portion of the compost samples, 50 to 100 g been taken and aerobically dry, these parts being manually separated and weighed.

Bulk density: It was estimated by cylinder method according to a study [6].

Moisture content: It was estimated by the weighted method according to a study [6].

Particle size distribution analysis: The particle size was estimated by mechanical analysis of the particles by using a set of sieves with different diameters. Estimating the weights of the particles passing through each sieve and then calculating their percentage in relation to the sample weight used in the analysis.

Water holding capacity: This property has been estimated by calculating the weight of the water that the particles absorb when saturating, by taking a certain weight from the physically and aerobically composite sample and placing it in a known weight or plastic container with holes at the bottom, then placed in a small box with water and left to saturate the water for a sufficient period (24 hours) Then it is left to drain the excess water by gravity, then take that sample and weigh it again as it is saturated and by subtracting the two weights we get the amount of water that the compost maintains and then the percentage of the amount of water can be known and it represents its ability to hold water.

Second, estimation of chemical properties

pH: Estimated by pH Meter (Model LF - Digi-550 30T), Germany, manufacturer W.T.W in extract 1: 2.5 compost and water.

Electrical conductivity (the presence of dissolved salts): By EC Meter (Model LF - Digi -330T), Germany, the manufacturer W.T.W, the estimated pH was through the same extract been taken for the electrical conductivity, pH being estimating at a temperature of 25°C, and its units dm/m.

The organic matter (the percentage of the organic matter): Estimated by the method of dry burning according to a study [7].

Total organic carbon percentage: The total organic carbon percentage in compost, is estimated by dividing the percentage of organic matter obtained by 1.724

Total nitrogen percentage: The percentage of total nitrogen was estimated using the Keldahl method according to a study [7].

Total phosphorous: Total phosphorous was extracted by dry burning and magnesium nitrate. From the phosphorus quantification, by the blue molybdenum method. and reading by a color grading apparatus according to a study [7].

Total potassium: It was extracted by the method of dry burning and it was quantified on the flame analysis apparatus according to a study [7].

Trace elements and heavy metals: It was extracted by dry burning method, and it was estimated on the atomic absorption device (Model/AA - 6601 F, AA - 670 F, SHIMADZU, JAPAN) [7].

Results and Discussion

Properties

From the results it is clear that the bulk density on the basis of wet weight ranged between 0.52 and 0.7 with an average of 0.6 g/cm³ during the study. The bulk density on the basis of dry weight was between 0.17 and 0.39 and an average of 0.24 g/cm³ during the study. The percentage of moisture content based on wet weight ranged between 31.25 and 42.18, with an average of 36.87% during the study. The percentage of moisture content on the basis of dry weight was between 45.68 and 73.01 with an average of 59.27% during the study. Looking at the data in Table 1 it is clear that the bulk density varies with time and accordingly the moisture content, which reflects the nature of the materials entering the plant with time.

Table 1: The bulk density and moisture content of the compost throughout the study.

Table 2 shows the monthly averages of the percentages of glass and plastic, from these results it is clear that the percentage of glass was between 5.62 and 13.1 with an average of 8.31% during the study, while the plastic was ranged from 1.61 and 5.40 with an average of 3.42% during the study.

Table 2: Percentage of foreign matters in the compost produced at Sawani plant throughout the study.

Through these results and their comparison with some international standards and specifications shown in Table 3, it is clear that these averages exceed those levels in Australia, Austria, Belgium, Germany, Italy, the Netherlands, Switzerland and UK, given that these countries have what is called a source-screening program that does not allow mixing waste with each other. This is consistent with the results obtained for the foreign matters content [8].

Table 3: Maximum Limits of foreign matters in the Compost Specifications produced from Municipal Solid Waste in Australia and Some European Countries.

Results of monthly averages for the particle size distribution and the percentage of water holding capacity are listed in Table 4. From these results, it is clear that the percentage of particles greater than 32.2 mm ranged between 0.11 and 1.14 with an average of 0.58%, while the percentage of particles greater than 8 mm ranged between 2.23 and 8.7 with an average of 5.54% during the study period. The percentage of particles greater than 4 mm ranged between 22.6 and 51.5 with an average of 38.06% during the study period, and finally, the particles of less than 4 mm ranged between 25.4 and 58.6 with an average of 41.9% during the study [9-15].

Table 4: Average results of the particle size distribution and the water holding capacity of the compost produced at Al Sawani plant throughout the study period.

The percentage of water holding capacity was between 79.34 and 115.43, with an average of 100.4% during the study [16-20].

It is clear from Table 4 that the average size of particles less than 4 mm constitutes the highest percentage, then followed by particles greater than 4 mm, then particles larger than 8 mm, then particles greater than 32.2 mm, and thus the percentage of water holding capacity varies according to the different particles averages and according to the different foreign matters. The other is that the difference is due to the heterogeneity of the raw organic matter and its nature and source over time, in addition to the immaturity of the produced compost [21-25].

The chemical properties of the compost produced from Sawani plant have also been studied. These properties included pH, EC, total organic carbon, organic matter, total nitrogen, total phosphorous, total potassium, the carbon to nitrogen ratio, Trace elements (Fe, Mn, Cu, Zn) and heavy metals (lead, mercury, nickel, chromium, cobalt, cadmium, arsenic) [26-35].

The results showed pH was between 6.46, 7.26 with an average of 6.6, while the results of EC ranged between 12.68 and 16.13 with an average of 14.57 dm/m during the study at a temperature of 25°C. we can conclude that, the pH is considered to be in the desired range while there is an increase in the values of EC in the compost, which does not always suffer from the high content of salts, so the high values of the EC may be attributed to the organic acids in the Compost which can reduce its maturity [36-40].

It has been clear from the results that, the percentage of total nitrogen ranged between 0.327 and 0.91 with an average of 0.77%, while the results of total phosphorous ranged between 7.18 and 373.2 with an average of 82.3 mg/kg during the study, and the total potassium ranged between 2800 and 4867 with an average 3866.7 mg/kg (Table 5).

Table 5: The monthly average of the concentrations of total Nitrogen, total Phosphorus and total Potassium throughout the study.

It appears from these results that the content of the compost samples from the nutrients is very low, therefore it is not advisable to rely on it as a fertilizer in providing all the plants' needs with these nutrients, especially when applied at low rates, but it can be used as a conditioner for different soil properties. As for the results of total carbon, organic matter, and carbon to nitrogen ratio indicates that the percentage of total organic carbon was between 18.67 and 27.96 with an average of 21.13%, while the average of organic matter was between 32.2 and 48.2 with an average of 37.87%. The carbon to nitrogen ratio was between 1:23 and 1:85 with an average of 1:32. It appears from these results that the average percentage of the organic matter is good and that the carbon to nitrogen ratio is high, therefore applying this type of compost as a soil conditioner will keep its effect on the soil for a long time due to the presence of this feature, which works with other factors to slow the composition process, thus helps to reduce the periods and amount of application rates [41-45].

The monthly averages of the concentrations of the Trace elements indicate that the total Fe concentration ranges between 1211.5 and 2403.8 with an average of 1906.7 mg/kg, while Cu results were between 61.36 and 160.1 with an average of 96.40 mg/kg. The results of Mn ranged between 64.13 and 112, with an average of 96.04 mg/kg, and Zn results were between 213 and 453, with an average of 313.28 mg/kg (Table 6).

Table 6: Monthly averages of the concentration of Fe, Cu, Mn, and Zn thorough out the study period.

It is clear that, the monthly averages of the concentration of the heavy metals show the results of lead were between 127.3 and 323 with an average of 171.86 mg/kg, and the results of nickel were between 4.97 and 10.56 with an average of 7.5 mg, kg, while the results of chromium ranged from 7.16 to 21.7 With an average of 14.48 mg/kg. The results of the cobalt ranged from 0.5 to 2.93 with an average of 1.90 mg/kg, while cadmium had results from 0.1 to 0.9 and an average of 0.49 mg/kg. Also, arsenic results were between 1.57 and 5.9 and an average of 3.8 mg/kg, while the results of mercury were ranging from less than 0.1 to 49.26 with an average of 13.4 micrograms/kg [46-50].

When comparing the results of the heavy metals during the study and their levels of the approved quality specifications for the compost produced from the municipal solid waste in some, we can notice from Table 7 that the average value of the arsenic is less than that in the Netherlands and Canada, as is the case In cadmium, chromium, nickel and cobalt (there are no specific levels in the Netherlands and some other countries), and nickel, except copper and zinc they are slightly more than they should be in the first degree in the Netherlands and less than they should be in the first and second degrees in all other countries. Likewise, lead is less than the second degree and more than the first degree in the Netherlands, while it exceeds than the two grades in Canada. Mercury is much lower than all grades in the Netherlands and Canada.

Table 7: Comparing the results of the heavy metals obtained with their levels in the compost produced from the MSW in some countries by mg/kg.

Conclusion

It was found through this study that the compost content of foreign matters such as glass and plastic is high, due to the lack of an accurate segregation program that limits or reduces the proportions of these materials in the final product during manufacture, which reduces its quality. Therefore, it is advised to pay attention to the processes of sorting and removing foreign matters to improve the quality of the produced compost.

It is also noted that the compost does not reach the degree of complete maturity (stability), as the emission of unpleasant odors from it indicates the presence of many technical problems related to the various stages of production, and the lack of control over the conditions for the success of this process (conditions of composition) in terms of commitment to ventilation (periods of stirring), Humidity, temperature, carbon to nitrogen ratio, particle size and other factors, resulting in a high compost content of phytotoxic compound.

It is also generally observed that the concentration of nutrients needed for plant growth is low, which is not recommended as a fertilizer to provide plants with their needs of these elements. Perhaps the advantages or features of this compost is the low levels of heavy metals comparing to its levels in some western and other industrialized countries.

REFERENCES

1. Malinger F, Weissteiner C. Results of an evaluation questionnaire. EU Compost Workshop. Federal Ministry of Environment, Vienna. 1999.
2. Warman PR, Havard KA. Yield, vitamin and mineral contents of organically and conventionally grown carrots and cabbage. Agriculture, Ecosystems & Environment. 1997;61(2-3):155-162.
3. Leita L, De Nobili M. Water-soluble fractions of heavy metals during composting of municipal solid waste. Journal of Environmental Quality. 1991;20(1):737-738.
4. Kehres B. Concerning quality of compost from various sources. Doctoral Dissertation, Kassel University. 1990.
5. Bildling meier W. Schwermetallen in Haus mull-Herkunft-schad wirkung. Analyses. Thesis paper. (Heavy metals in Household Wastes-Origin, Harm full effects and Analysis). 1987.
6. Black CF, Evans DD, Ensminger LE, White JL, Clark FE. Methods of Soil Analysis Part 1. American Society of Agronomy, Inc, publisher Madison, Wisconsin. 1965.
7. Chapman HD, Pratt PF. Methods of analysis for soils, plants and waters. Soil Science. 1962;93(1):68.
8. Brinton WF. Compost quality standards and guidelines. Final Report by Woods End Research Laboratories for the New York State Association of Recyclers. 2000.
9. Aggelides SM, Londra PA. Effects of compost produced from town wastes and sewage sludge on the physical properties of a loamy and a clay soil. Bioresource Technology. 2000;71(3):253-9.
10. Standards Australia International. Composts, soil conditioners and mulches. Standards Australia International. AS454-1999.
11. Bazzoffi P, Pellegrini S, Rocchini A, Morandi M, Grasselli O. The effect of urban refuse compost and different tractors tyres on soil physical properties, soil erosion and maize yield. Soil and Tillage Research. 1998;48(4):275-86.
12. Bengtson GW, Cornette JJ. Disposal of composted municipal waste in a plantation of young slash pine: Effects on soil and trees. Journal of Environmental Quality. 1973;2(4):441-4.
13. Bernai MP, Paredes C, Sanchez-Monedero MA, Cegarra J. Maturity and stability parameters of composts prepared with a wide range of organic wastes. Bioresource Technology. 1998;63(1):91-9.
14. Berset JD, Holzer R. Organic micropollutants in Swiss agriculture: distribution of polynuclear aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) in soil, liquid manure, sewage sludge and compost samples; a comparative study. International journal of environmental analytical chemistry. 1995;59(2-4):145-65.
15. Bezdicek D. Compost quality: New threats from persistent herbicides. Agrichemical and Environmental News. 2000;174:9-13.
16. BGK. Methods Manual for Compost Analysis. German Compost Quality Agency. 1994.
17. Bingham FT, Page AL, Mahler RJ, Ganje TJ. Growth and cadmium accumulation of plants grown on a soil treated with a cadmium-enriched sewage sludge. Journal of Environmental Quality. 1975;4(2):207-11.
18. BioAbfv. German Bioabfallver ordunung. Bundesges etzblatt G5702 Bonn 28. Sept.1998 (revised March 1999) Ordinance: Ultiliation of Bio Wastes on Land Used for Agriculture, Silvicultural and Horticultural Purposes. 1998.
19. Candinas T. Minimum Quality Standards for Compost. FAC-EDMZ3000Bern. 1995.
20. Candinas T, Golder E, kupper T, Besson J. Nutrients and Contaminants in Composts. Agrarforschung. 1999;6:421-424.
21. James GC, Sherman N. Microbiology and laboratory manual, rockland community college, suffern, New York. 1999.
22. CASZ. Standards for Compost. Briefing Note, UK Composting Association. 2000.
23. CBNS. Report by Center for Biology of Natural Systems, Washington Univ., St Louis. 1975.
24. CCC. Compost Standards Review. Compost Council of Canada. 1999.
25. De Haan S, Lubbers J. Huisvuilcompost en zuiveringsslib als organische meststoffen voor bouwlandgewassen op een zware rivierkleigrond in de Bommelerwaard, in vergelijking met stalmest, groenbemesting en turfmolm= Refuse compost and sewage sludge as organic manures for arable crops on a heavy fluviatile clay in the Bommelerwaard, compared with farmyard manure, green manure and peat moss. IB; 1984.
26. Delschen T. Impacts of long-term application of organic fertilizers on soil quality parameters in reclaimed loess soils of the Rhineland lignite mining area. Plant and Soil. 1999;213(1-2):43-54.
27. DHV. Composting in the European Union. Final Report. DHV Euro Commission DGHI – Revised Rule BRL K256 / 03; Netherlands. 1999.
28. Diener RG, Collins AR, Martin JH, Bryan WB. Composting of source-separated municipal solid waste for agricultural utilization–A conceptual approach for closing the loop. Applied Engineering in Agriculture. 1993;9(5):427-36.
29. Duggan JC, Wiles CC. Effects of municipal compost and nitrogen fertilizer on selected soils and plants. Compost Science. 1976:24-31.
30. EPA. CFR-40 chap 503 proposed Rule. Sludge Guidelines. Sep1989Fedral Register, Revised and published as CFR-40 chap 503.Final Rule. Feb1993. 1989.
31. Epstein EL, Taylor JM, Chaney RL. Effects of sewage sludge and sludge compost applied to soil on some soil physical and chemical properties. Journal of Environmental Quality. 1976;5(4):422-6.
32. Fricke K. Basis of Biowaste Composting. Dissertation Kassel University. Verlag Die werks tadt. 1988.
33. Jourdan B. Towards recognition of the degree of rotting of municipal waste and sludge -MSW composts. Stuttgarter Reports 30. Institute of Waste Management Univ Stuttgart. 1988.
34. Kelling KA, Walsh LM, Keeney DR, Ryan JA, Peterson AE. Afield Study of the Agricultural Use of Sewage Sludge: II. Effect on Soil N and P. Journal of Environment Quality. 1977c;6:345-352.
35. Kladivko EJ, Nelson DW. Surface runoff from sludge-amended soils. Journal (Water Pollution Control Federation). 1979:100-110.
36. Leinweber P, Reuter G. The influence of different fertilization practices on concentrations of organic carbon and total nitrogen in particle-size fractions during 34 years of a soil formation experiment in loamy marl. Biology and Fertility of Soils. 1992;13(2):119-124.
37. Loe bel KJ, Beauchamp EG, Lowe S. Soil modification and plant growth on a calcareous sub soil treated with partially composted “sludge -leaf “mixture. Reclamation and Revegetation Research. 1982;1:283-293.
38. Maynard A. Nitrate leaching from compost amended soil. Compost Science and Utilization. 1993:65-72.
39. Mays DA, Terman GL, Duggan JC. Municipal compost: Effects on crop yields and soil properties. Journal of Environmental Quality. 1973;2(1):89-92.
40. Naylor LM. Compost quality assurance for dependable markets. InNational Extension Compost Utilization Conference Proceedings. Minneapolis, Minnesota. 1993:29-40.
41. Pagliai M, Antisari LV. Influence of waste organic matter on soil micro-and macrostructure. Bioresource Technology. 1993;43(3):205-13.
42. Piccolo A, Mbagwu JS. Effects of different organic waste amendments on soil microaggregates stability and molecular sizes of humic substances. Plant and Soil. 1990;123(1):27-37.
43. Reider CR, Herdman WR, Drinkwater LE, Janke R. Yields and nutrient budgets under composts, raw dairy manure and mineral fertilizer. Compost Science & Utilization. 2000;8(4):328-339.
44. Sikora LJ, Yakovchenko V. Soil organic matter mineralization after compost amendment. Soil Science Society of America Journal. 1996;60(5):1401-1404.
45. Stöppler-Zimmer H, Petersen U. New results concerning the application of compost in plant cultivation, 1. International Symposium: “Biological Waste Management—A Wasted Chance 1995:11.
46. Tate III RL. Soil organic matter. Biological and ecological effects. 1987.
47. Tester CF. Organic amendment effects on physical and chemical properties of a sandy soil. Soil Science Society of America Journal. 1990;54(3):827-831.
48. Vogtmann HK, Fricke, Kehres B, Turk T. Biowaste composting. Hessen Ministry for Environment, Wiesbaden. 1989.
49. Wiemer K, Kern M. Compost international. Abfall Wirtschaft, (Technical Series) 2. 400PP.University of Kassel. MICB aezaverlag. 1989.
50. Zan FD, Baruzzini M. Candotti. Yield responses of four different crops to compost application. In: De Bertolodi, et al. (eds.) compost: Production, Quality and Use. Elsevier Applied Science, London. 1987:781-784.