Abstract

Increased urbanization is accompanied by the generation of large amounts of garbage, which includes both biodegradable as well as non­biodegradable wastes. This study involves designing, planning and effective implementation of a scientifically managed Solid Waste management System with proper segregation, collection, transportation, processing and disposal techniques. The emphasis is on the segregation of the waste into organic and recyclable fractions at the source and composting of the wet waste aerobically. The study also includes use of digested sludge from a biogas plant as manure. This compost and digested and dried sludge has been tested for the presence of essential nutrients and absence of heavy metals and pathogenic bacterial contamination. Experiments using this compost and sludge on various vegetables and horticultural crops show that when used either singly or in combination these organic manures if applied scientifically, can replace the chemical fertilizers as supplementary nutrient source.

Combating Solid Waste - A Fruitful Strategy

Ms. Shyamala K. Ivlani, Ms. C. Sethulaksmi

Mr. George Verghese, Dr. V .C. Reddy

Environmental pollution is caused by solid, liquid and gaseous waste. Of these, solid waste poses a serious problem as the available technologies are not adequate for their management. The increased generation of solid waste is not only posing problems in storage, collection and transport but also in final treatment and disposal. For these reasons there is a need for development of technology of solid waste treatment that prevents or substantially reduces pollution of the environment. Some of the existing solid waste treatment methods practiced include: sanitary landfilling, incineration, pyrolysis, conversion to biogas, refuse derived fuel (RDF), recycling and reuse, disposal of refuse into the sea, fuel pelletization, composting, vermicomposting etc. The choice of any solid waste treatment method depends on suitability of waste, degree of pollution prevention and economic viability of technology. For Indian cities, refuse composting is most suitable as it contains 70 to 80% of biodegradable organic waste. The method is pollution free and economically viable. Segregation of waste at source is the most important component of effective waste management. Unsegregated city waste that contains paper, plastic, glass, rubber, leather, coal, crackers, metal, rags, toxic materials, if composted would render the compost unsuitable and toxic for agricultural use. Most of the studies done have shown that source separation of municipal solid waste, followed by biological treatment of the biodegradable fraction, composting or anaerobic digestion are beneficial with respect to recycling most of the nutrients and is also environment friendly. The compost made from unsegregated garbage has been found to be contaminated with heavy metals. The comparison of heavy metal concentrations in compost made from segregated and unsegregated garbage is shown in the Table 1.

Table: 1 Heavy metal concentrations in mg/100gm in compost prepared from segregated and unsegregated wastes

Aerobic. Anaerobic and Vermiciomposting methods are mostly adopted for composting of solid waste. Recovery of valuable resource of non-biodegradable like metals, paper and plastic have been sustained by informal sectors (Shyamala et al., 1997). This study deals with the recycling of waste and the use of recycled organic waste as organic amendment to improve the productivity status of the soil.

Compost and sludge as organic manures 
Application of organic manures improves the nutrient status of soils prevents soil deficiencies, improves soil carbon and phosphorus status, soil structure and reduces soil erosion (katyal et al,. 1993). Studies have shown that water soluble cations like C', K, Mgz', Fe'', A1³', Zn²' diminished in soils applied with composted solid urban waste and increase in enzymatic activities of urease, protease, casein-protease, phosphatase, dehydrogenase etc. (Fortun et al., 1997, Guisquiani et al., 1995). Improvement of biological quality of soil is reported by organic amendment of soil through applications of various urban wastes (municipal solid waste, sewage sludge and compost) indicating the activities of soil microorganisms (Pascual et al., 1997). Studies on the effect of mycorrhizal inoculation and organic matter fertilization on microbial activity and nutrient release in soil have shown that viable microbial counts of phosphate dissolving bacteria and dehydrogenase activity is greatly enhanced by organic manuring and high positive co­relation between viable microbial counts and dehydrogenase activity in control soil, biogas residues and sludge treatments is observed. (Estefanous et al., 1997).

The recent decline in rice and wheat production reported from some regions in India have refocused the attention on organic manures which not only have synergistic effects with fertilizers and helps make them more efficient but also improves soil physical and biological properties and thereby helps in making highly productive cereal cropping systems sustainable (Rajendra Prasad et al., 1998). Sulphur is used as an organic fungicide but soil enrichment with organic fertilizer and soil drainage to produce `healthy soil' is also seen as a method of disease control, especially against root rot (Brener et al., 1993). Long term use of organic farming has shown to increase nitrogen, organic matter and phosphorus in soil. Microbial biomass levels were consistently higher while plant parasitic nematodes are consistently lower (Scow et al., 1994). Certain types of soil like calcareous soil can also be amended with urban wastes compost which results in increased porosity, increase in total and humified organic carbon, lead, copper and zinc and enzymatic activities (Guisquiani et al., 1995). Many reports have shown that compost can be put to good use as fertilizer when applied to some field crops like Sesame, Papaya, Lepidium sativum (garden cress) and other horticultural crops (Abdel-Sabour et al., 1996, Ayuso et al., 1996, Basso et al., 1995). Sewage sludge has been found suitable as a fertilizer for certain crops and for amending soils. (Pascual et al., 1997_> Ayuso et al., 1996, Poletschny et al., 1994). Biogas sludge when applied to crops like ragi, garlic etc. has resulted in higher mean yields than FYM, as it has higher percentage of total N,P2O5, K2O and organic carbon than Farm Yard Manure (FYM), (Ranganna et al., 1991). Transition from conventional to organic and low input farming systems has proved more profitable with lesser inputs (Klonsly et al., 1994). 

METHODOLOGY

Composting of Domestic Solid Waste

Our projects have all been carried out in residential areas. Residents of the area were educated about Solid Waste Management and importance of segregation of waste through audio-visuals, pamphlets, posters and public meetings. Composting pits were constructed in a suitable place in a park, with the permission of Bangalore City Corporation (BCC) and Bangalore Development Authority (BDA). Waste retrievers were trained to collect the segregated waste i.e. Biodegradable and Non-biodegradable wastes separately. Biodegradable wastes were taken to composting pits for processing and non-biodegradable wastes were sold to the recycling agents. 

Composting Process

The collected organic waste was taken to the composting site. The organic waste was evenly spread and covered with a layer a of leaf litter in the pits daily. The material in the pit is turned with a rake once in 2-3 days to hasten the process of aerobic composting. The heat generated in the compost heap reaches up to 60"c and the moisture level is maintained to 50-60% by sprinkling water. The whole process takes 40-45 days for complete degradation and the final compost is dark brown granular material with an earthy smell (Shyamala et al,. 1994). The aerobic compost has been chemically analyzed and the results are tabulated in Table 2.  

Table : 2 Physico-chemical properties of aerobically composted urban solid waste was analyzed before conducting the field trial. The soil was red.

 
Dried sludge from Biogas plant

A community toilet complex with 20 units is linked to a biogas plant where the night soil is anaerobically digested to produce biogas. The digested sludge is led to sludge drying beds with FRP sheet roofing. The drying beds facilitate partial drying of the sludge by evaporation and partly by draining of the waste-water through the sand layer at the bottom. The settled sludge after sun drying was chemically analyzed and the results have been tabulated in Table 3.

With a view to assess the manurial properties of the compost and sludge on the soil quality, field trails were conducted using digested sludge. Field trials were conducted on banana cultivar yelakki during 1997­1999 at Shobha Farm, Narasapur near Bangalore to find out the effect of sludge as manure. The sludge was found to be rich in nitrogen and phosphorus but poor in potassium. It was alkaline in reaction and hence suitable for acidic soils. A composite soil sample drawn from the experiment site was analyzed before conducting the field trial. The soil was red sandy loam with a pH of 7.13 and EC of 0.26 dsm^-' and medium in fertility. Soil properties as influenced by the sewage sludge application is shown in Table 3. Land was ploughed twice and harrowed

once to bring fine tilth. Pits were opened at a spacing on 8'x 8'. The size of pit was 2'x 2'x 2'. Uniform sized suckers of banana cv. yelakki were planted in October 1997 in the pits after applying the following treatments.

The treatments were replicated 9 times and laid out in the field in a randomized block design (RBD). Irrigation from tube well was given as and when required. About 2-3 suckers per clumps were allowed to grow and the rest were removed. Observations made included plant height, stem girth, days taken to harvest, bunch and fruit yield per bunch.

Table: 4 Soil Properties as influenced by sewage sludge application in Banana  

Table: 5 Effect of digested night soil sludge and farmyard manure on plant height, stem girth, harvest time and yield of banana (Average of two years)

Urban Garbage Compost

Urban garbage compost was tested on

1) Tomato @ 10, 20 and 30 tons per hectare in a field trial conducted at Whitefield, Bangalore during summer of 1997. The trial was conducted in a randomized block design with ten replications. The compost was applied in furrows opened 75 cm apart. About thirty days old Pusa Ruby seedling of tomato were transplanted 60 cm apart on 20th January, 1997. Irrigation and weeding were done as and when necessary. Staking of plants was done after 30 days and training of plants continued up to 60 days from transplanting. Observations like

plant height, number of fruits per plant, fruit weight and fruit yield per hectare was recorded from each plot.

2) Sequential cropping of vegetables

During Kharif  1997, brinjal, bhendi and beans were raised followed by radish, beetroot and carrot in summer 1998. After segregation of garbage from Bangalore City , decomposable materials were composted and applied@ 15, 20 and 25 tons/ha for each crop. All field trials were conducted in a randomized block design with ten replications.

A composite soil sample was drawn from the experimental site for further analysis. It was red sandy loam with a pH of 7.13, EC 0.26 dsm^-', organic carbon 0.61%, available N 0.009%, available, P₂0₅ 0.008% and available K of 0.0228%. Soil was low in carbon, available N, P and K. The compost was incorporated into soil prior to sowing/transplanting. Irrigation was given whenever necessary. Fields were kept free of weeds. No plant protection measures were used. Slight bacterial wilt attack was observed in brinjal due to heavy rainfall. However, the condition was improved on providing drainage. Crops were harvested and the data on the yield was analyzed statistically.

RESULTS AND DISCUSSION

Application of compost@ 20 t/ha increased the fruit yield of tomato (14 t/ha) significantly over 10 tons compost per ha (7.3 t/ha) but was on par with 30 tons compost per ha. Similarly plant height, number of fruits per plant and fruit weight significantly increased by 20 tons of compost and not by the highest dose of 30 tons of compost (Table 7).

Improved plant height, number of fruits per plant and weight per fruit were mainly responsible for increased tomato yield associated with the application of 10 tons compost. Quality of fruit as judged by the TSS (brix), acidity and ascorbic acid content were improved by the application of 20 tons compost per hectare. While application of 30 tons of compost had not improved the quality of fruit (Table 8) (Tikko et. al. 1989)_> it was observed that there was no significant increase in TSS of tomato by increasing nitrogen level from 60 to 120 kg per hectare. The land on which the experiment was conducted had not been used for growing any crops and had only some coconut trees. No supplement had been applied to the soil before the experiment was conducted. The soil chemical properties were analyzed before conducting the trial and also after the harvest of tomato crop (Table 9).

Soil pH had increased from 6.95 to 7.6 by the application of compost since the compost was alkaline (pH 8.2) in nature. Besides EC was also

higher with compost application. This is in conformity with the findings of Epstein et.al., (1976). Organic carbon content of the soil is the key factor to maintain sustainability of crop production. Application of compost to tomato crop raised the residual organic carbon from 1.14% to 1.93%. This was reflected in higher available phosphorus with compost application (51:8) compared to its status before conducting the trial (10.5). However the available potassium level was lowered (67.5) by the application of lower level of compost (10 tons/ha). Residual K was improved by the higher levels of compost (20 and 30 tons/ha) application. Mehta and Daftardar (1984) obtained similar increase in yield with urban garbage compost application.

Table: 7 Effect of compost levels on plant height, fruit number, fruit weight and yield of tomato cv Pusa Ruby as influenced by garbage compost.

Table: 8 Effect of garbage Compost levels on quality of Tomato fruit (cv Pusa Ruby)

Application of 20m ton if compost per hectare produced significantly higher yield of 92.9 and 78.9 quintals per hectare respectively in brinjal and behind crops (Table 10) compared to 15 tons of compost (26,6 and 34.s quintals/ha, respectively) However, the crop yield did not different between 20 and 25 tons of compost application. while, beans responded significantly up to 15 tons of compost (108 quintals/ha). However further increase in compost application to 20 or 25 tons did not increase the beans yield significantly. Similar increase in yields of tomato, barley and lettuce crops was observed by the application of garbage compost (Vlamis and williams,1972).

During the 1998 summer, it was found that the higher application of compost produced  significantly higher yields of beetroot and radish as compared to 15 tons applicatioon(Table11)

Further increase in the compost to 25 tons/ha did not cause significant variation in yield while the yield of carrot was significantly higher (66 quintals/ha) at 25 tons of compost/ ha. Analysis of soil reveals that there was increase in the pH, EC, organic carbon and nitrogen by increased compost dose (Table 12). Also they were higher than the status found before conducting the field trains. In a review, Gallardo Lara and Nogales (1987) concluded that compost is slightly alkaline and increases soil pH and electrical conductivity. Hence garbage compost is found to be best for acidic soils since it acts as a buffering agent.

Table: 9 Chemical analysis of the Soil from the experimental site, Whitefield

A major portion of the urban garbage is organic in nature and compost prepared from this fraction forms a good source of nutrients for the plants. Our studies show that urban garbage needs to be segregated at the source and this is the most important step before subjecting the waste to any kind of treatment. Compost prepared from unsegregated garbage is shown to have toxic elements like heavy metals, which could be bio-magnified along the food chain (Table 1). Heavy metals can also contaminate ground water aquifers and can cause direct effect on consumption both on animals and humans. The mineral composition of the compost needs to be analyzed to find the percentage of the essential nutrients and heavy metal contamination (Table 2 & 3) required for plant growth. Untreated sewage when used for agriculture, over a period of time, may cause metal accumulation in soils to such an extent that they may become toxic to plants (Kirkham et al., 1983). Compost and treated sludge from biogas plants are being successfully used as a substitute for chemical fertilizers. Such organic manures are natural fertilizers that help improve soil structure, aeration, organic content, macro and micronutrients and microbial life in soils.

Treated human night soil has proved to be a very good source of nutrients for plants (Poletschny et al., 1994). Treated sewage (domestic and industrial) needs to be analyzed for the presence of pathogens, toxic metals etc. Long-term use of untreated sewage could lead to mutagenic and carcinogenic effects (Janoska-B et al., 1996). Large scale sewage treatment plants need to follow primary treatment by using appropriate methods like heavy metal bio-leaching and stabilization of municipal sludges for example, using Thiobacillus strains to oxidize elemental Sulphur to Sulphuric acid. (Benmoussa-H et al., 1994). Comparisons between Organic farming and low input sustainable Agriculture (LISA) practices reveals that use of synthetic fertilizers and pesticides is largely prohibited in organic farms but allowed to some extent by the LISA systems (Horticultural Science, 1992, 27:7, 759-760).

CEE has taken up this issue by combining efforts on one hand to motivate and educate public about responsible solid waste management practices which involves reducing, reusing, and recycling waste while on the other hand it coordinates with various government and research institutions in evolving strategies to safely collect and recycle/dispose waste. Solid waste management is the responsibility of every citizen and can be properly implemented only by collective effort.

Table: 10 Effect of Compost on the yields of brinjal, bhendi and beans

Table: 11 Yield of Beet root, Carrot and Radish as influenced by garbage compost

CONCLUSION

Table: 12 Soil properties after Kharif 1997 and summer 1998 trials on vegetables.        

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Research & Development Centre for Environment Education, India  

About AAWaM

The Ministry of Environment & Forests, Govt. of  India (MoEF) with the German Technical Cooperation (GTZ) has started a project in many small and big towns of India termed Eco-cities which are well known pilgrimage or tourist destinations having large floating populations, for proper and appropriate management of domestic and other urban waste. This project called Achieving Action in Waste Management' (AAWaM) hopes to not only achieve public participation in waste management but also develop a methodology which can be spread throughout the country to achieve cleaner cities and improved health conditions. Central Pollution Control Board (CPCB), German Technical Cooperation (GTZ) and Centre for Environment Education (CEE) will be jointly working on this project in the next one and half to two years. Adisory Services in Environmental Management (ASEM), One World and the German Federal Ministry for Economic Cooperation and Development are also important partners of the Eco-cities programme.