Derbal Kerroum, Bencheikh-LeHocine Mossaab and Meniai Abdesslam Hassen

University Mentouri Constantine,

Algeria

1. Introduction

The pollution of water, air and soil by municipal, industrial and agricultural wastes is a major concern of public autorithies who imperatively have to encourage the development of effective and non expensive treatment technologies. Although it is not recent, the process based on the anaerobic digestion (bio-methanisation) for the treatment of the waste organic fraction, is getting very attractive from the environmental and the economical points of view. It consists of a biological degradation of the organic matter, under anaerobic conditions, where a biogas, mainly methane (CH4) is evolved, and hence providing a renewable source of energy which may be used in the production of electricity and heat.

Generally various types of residual sludges and solid wastes are generated by human activities. They are composed of organic matter which may or may not be easily biodegradeable, inorganic matter, inert soluble and non soluble matter, toxic matter, etc. In order to treat these solid wastes, it is first required to characterise them and second to choose a treatment mode depending on their types and their possible final destinations. According to the physical state, one may distinguish solid wastes (dehydrated sludges, domestic wastes, etc.), liquid wastes (effluents from food, fresh liquid sludges, etc.) and suspensions (sludges from water treatment plant). Classification in terms of the sources may be as follows: [18]

mineralised organic matter. The sludge characterisation is essential for the choice of the most adequate treatment method as well as for the prediction of each treatment stage performance. Generally distinction is made between primary sludges which are recovered by simple waste waters decantation, and are of high concentrations in mineral and organic matter, and the biological or secondary sludges resulting from a biological treatment of waters. These latter have different compositions, depending on the nature of the degraded substrate, the operation load of the biological reactor and the eventual stabilising treatment.

For the treatment of the different pollution types, vvarious techniques and processes of different chemical, biological and physico-chemical natures as well as a coupling of the last two, are developed. The treatment and the final elimination consist of a sequence of unit operations with a great number of possible options among which the best one is to be chosen, taking into account the upstream (nature, characteristics, and waste quantities) and downstream (local possibilities of final eliminations) constraints as well as the cost.

The present study is more concerned by the biodegradable organic solid wastes which are characterised by a high organic matter concentration, recommanding a biological treatment.

One of technologies to carry out the treatment of the organic fraction of this organic waste is anaerobic digestion (bio-methanization, this process is presented with more details in the next sections of this chapter), which consists of a biological degradation in an anaerobic phase of the organic matter into biogas with a high methane percentage. This technology is becoming essential in the reduction of organic waste volume and the production of biogas, a renewable source of energy. It can be used in a variety of ways, with a heating value of approximately 600 -800 Btu/ft and a quality that can be used to generate electricity, used as fuel for a boiler, space heater, for refrigeration equipment, or as a cooking and lighting fuel.

On the basis of this study, it is expected that the UASB reactors packed with steel elements may be applicable to treat UF whey permeate to produce biogas with high CH4 content. The COD removal efficiency, biogas productivity and CH4 content in biogas were enhanced by 11.4 — 17.0% (p<0.05), 1.67 — 2.15 m3 m3 d-1 (p<0.05), 8.3 — 17.2% (p<0.05), respectively, in the UASB reactor packed with steel elements compared to the control reactor performances. In this work, the maximum biogas production rate was 8.22 L d-1 in the reactor containing additional iron medium in contrast to about 4.2 L d-1 in the control reactor. Total phosphorus removal efficiency obtained in RFe was higher by 58.4 — 77.7% than in R0 (p<0.05). High iron concentration in the anaerobic granular sludge was not contributed to inhibit the activity of methanogenic bacteria. It should be pointed that during anaerobic corrosion process a protective layer on the steel surface can be formated to decrease phosphorus removal efficiency.

Biogas residue fibre film samples were prepared with the method of clean pulping and paper-making process. The optimization of the technological parameters were studied by the method of the central composite quadratic orthogonal rotational experiment, beating degree, grammage, rosin, bauxite and wet strength agent were selected as input variables, and dry tensile strength, wet tensile strength, degradation period were chosen as response functions.

Factors and its levels of experiment were shown in table 3-1. Experimental plan and results were shown in table 3-2.

Rungwe district lies between latitudes 8030 E and 9030 E and longitudes 330S and 340 S. It is one of the six districts of Mbeya Region, located in the Southern Highlands of Tanzania. The other districts are Kyela, Chunya, Ileje, Mbeya Rural and Mbozi. Rungwe district has a total area of 2211 sq. km of which 75% is arable land (URT, 1997). Of the remaining area, 44.5 sq. km is covered by forest while 498.3 sq. km is either mountainous or residential areas.

The district is one of the densely populated districts in Tanzania (URT, 2002) with a population of 307,270, which is equivalent to 139 persons per square kilometre with an annual growth rate of 0.9% (URT 2010). The district has limited natural vegetation which varies from upper montane forest at higher elevations to the wet woodland (Miombo) at lower elevations. Forestry reserve accounts for 43,749.9 ha and other forests about 65,813 ha (URT, 2008). In recent years, much of this natural vegetation has been cleared/transformed for agriculture, for habitation, and firewood. Most of the remaining natural vegetation is found in government forest reserves and in locally protected areas, though even these areas have been subjected to varying degrees of people driven disturbances.

Rungwe district put great importance to livestock development particularly dairy cattle as one of the major economic activities. In 2005 the district had 26,137 indoor fed dairy cattle with milk production estimated to be 41,000,000 litres per year. The district has 74,450 households and almost half of the households keep some cattle or pigs in their homestead with an average of between 2-6 cattle (Mwakaje, 2008). Smallholder dairy production is an important undertaking and, if adequately supported by appropriate policies and adaptive research technologies, it may contribute significantly towards the household economy, self­sufficiency in milk and national gross domestic product (Swai and Kimambo, 2011). Walshe et al (1991) comments that where there is access to a market, dairying is preferred to meat production since it makes more efficient use of feed resources and provides a regular income to the producer.

Promotion of smallholder dairy farming can solve the problem of rural poor accessing to clean energy like biogas.

The district is also famous for keeping pigs. Rungwe district has about 44,334 pigs which also contribute significantly to the household’s economy and nutrition.

Studies in several African countries, provides a rough sense of the likely economics of introducing biodigesters (Schwengels, 2009) where 2 cows or 1 cow and other livestock like pigs can be appropriate for a family to meet the need of cooking biogas while other research findings suggest that farming households, having 2 (zero-grazed) to 10 cattle or 8 to 40 pigs (or a combination) are enough to produce gas for a household. This means that available number of indoor fed dairy cattle of more than 26,000 and over 44000 pigs, the district can have the capacity of having more than 20000 biodigester, this is about 27% of the district’s households.

However, despite the high level of indoor fed dairy cattle in Rungwe District and the potential to generate biogas as well as the efforts to promote biogas use in the country since 1970s by the government and donors, biogas technology has not well developed in the district to date. The trend of biogas technology in the district shows that the technology started in 1993 when one person adopted installed a biogas plant (Mwakaje, 2008). In 1996, 12 households got the service by contributing half of the cost. This was a pilot project by the Danish Volunteers that intended to raise awareness of the technology. With the exception of the year 1996, adoption of the biogas technology has remained low and more or less declining (URT, 2005). Up to 2007 there were about 100 biogas plants, an equivalent to only 0.13% of the total households in the district. This is even more surprising as the district has limited fuelwood sources as well as other clean energy sources. Available information shows that the district has a demand of cooking energy of 600,000 m3 per annum, while the capability to supply is about 400,000 m3 (URT, 2005), a 33% deficit (Mwakaje, 2008). The scarcity of fuelwood has increased its cost in terms of purchasing price and time used for fetching (Mwakaje, 2008). The use of other clean energy like electricity and solar power is limited due to both cost and reliability (Mwakaje, 2008).

Why the pace of biogas adoption and use in the district has remained stagnant is the main interest of this study. Although, a study by Mwakaje (2008) highlighted some of the constraining factors, it was not exhaustive. The study focused more on the environmental benefits of adopting biogas technology while other equally important issues related to biogas use and adoption such as socio-economic, institutions; awareness as well as policies were not adequately explained. The main objective of the chapter was to come up with an understanding of the reasons for the stagnated biogas use in Rungwe district despite the availability of large number of dairy cattle and other livestock and in an area with highly inadequate fuelwood supply. Specifically, the chapter investigated issues relates to investment costs, expertise availability, role of institutions and policies in influencing biogas use and level of awareness of biogas use among the Rungwe dwellers. Findings from this study will add to the body of knowledge, inform policy makers, donors, service providers, environmentalists and researchers.

Controlled fermentation of biomass in biogas plants produces a gas that can be used to produce electrical and thermal energy on account of its high percentage of methane. The raw materials used in biogas plants or their main substrates, are often liquid manure, agricultural products, and some agro-industrial wastes. The biogas plant may use silage maize as one of its renewable raw materials, with the aid of wheel loader, the maize is fed into either a storage bin or solids feeder, which takes a filling up approximately once a day. Silage maize is rich in energy, and on account of it is high degree of production it is very well suited for use in biogas firms. The storage bin is equipped by hydraulic flow discharger that continuously feed the maize onto a conveyor belt. A scale under the conveyor belt registers the weight of the maize silage. Liquid manure is the most important basic substrate used in biogas plants, after short influence storage in big tank, it is pumped through pipes directly into the blending pumps beside the maize conveyor belt, at the same time the maize fall off from the conveyor belt into separators, which is equipped with two mixing rollers, in this way the maize silage is mixed before fermentation. With this technology, it is possible to supply several fermentation tanks (also known as fermenters and digesters) with fresh substrates even if they are not close together. Liquid wastes from the food industry are the third substrates used in biogas plants, as the availability of such wastes varies considerably, a large storage pit should be installed to integrate this into a whole serving to minimize smells and help to prevent epidemics. The liquid waste is heated with hot water into 70 °C in a tubular heat exchanger using a counter current process. After heating for one hour, the hydrogenation of the substrate is complete so that they can be poured into the fermenters. The fermenter is the place where the biogas is formed, the substrate are continuously stirred in order to prevent layers of materials forming at the top or on the bottom, hot water tubes heat the substrates to between 35 and 55 oC to accelerate the formation of methane. The substrate is in the fermenter for a period of around 30 days before it is filled into another fermenter for a further 30 days to complete the gas formation process. When fermentation is complete the thin liquid substrate is pumped into two reinforced concrete tanks, where it is stored until it can be brought out onto the fields.

Barbara Rincon and Rafael Borja

Instituto de la Grasa (CSIC), Avda. Padre Garcia Tejero, Sevilla,

Spain

1. Introduction

The evolution of modern technology for olive oil extraction has affected the industrial sector depending directly on the by-products obtained. The traditional three-phase continuous centrifugation process for olive oil extraction was introduced in the 1970s, notably to increase the processing capacity and extraction yield and to reduce labour. This three-phase manufacturing process of olive oil usually yields an oily phase (20%), a solid residue (30%) and an aqueous phase (50%), the latter coming from the water content of the fruit, which is usually defined as vegetation water. Such water, combined with that used to wash and process the olives, make up the so-called "olive mill wastewater" (OMW) and also contains soft tissues from olive pulp and a very stable oil emulsion (Borja et al., 2006). This process generates a total volume of traditional OMW of around 1.25 litres per kg of olives processed. Consequently, the three-phase centrifugation process caused an increase in the average mill size, a decrease in the total number of mills, increased water consumption and increased production of wastewaters.

The OMW composition is not constant either qualitatively or quantitatively and it varies according to cultivation soil, harvesting time, the degree of ripening, olive variety, climatic conditions, the use of pesticides and fertilizers and the duration of aging. The three-phase OMW is characterized by the following special features and components: intensive violet — dark brown to black in colour; specific strong olive oil smell; high degree of organic pollution (chemical oxygen demand — COD — values up to 220 g/L); pH between 3 and 6 (slightly acidic); high electrical conductivity; high content of poly-phenols (0.5-24 g/L) and high content of solid matter (Niaounakis and Halvadakis, 2004).

The annual OMW production of Mediterranean olive-growing countries is estimated to ranging from 7 million to over 30 million m3. This huge divergence of results can partly be explained by the fact that the production of olives varies from one year to another due to weather conditions and plagues that can affect the olive trees. The average total production amounts approximately to 10-12×106 m3 per year and occurs over a brief period of the year (November-March). Spain produced 20% of the OMW of the Mediterranean basin (2-3×106

m3/year) before the implantation of the two-phase extraction process in most of the Spanish olive oil factories, which represented an equivalent pollution of 10-16×106 inhabitants in the short milling period (Nioaunakis and Halvadakis, 2004).

The efforts to find a solution to the OMW problem are more than 50 years old (Borja et al.,

2006) . There are many different types of processes that have been tested: detoxification processes (such as physical, thermal, physicochemical, biological and combination of processes), recyclying and recovery of valuable components, production system modification, etc. However, none of the detoxification techniques on an individual basis allow the problem of disposal of OMW to be solved to a complete and exhaustive extent, effectively and in an ecologically satisfactory way. At the present state of OMW treatment technology, industry has shown little interest in supporting any traditional process (physical, chemical, thermal or biological) on a wide scale. This is because of the high investment and operational costs, the short duration of the production period (3-5 months) and the small size of the olive mills (Borja et al., 2006).

Evaluation of the feasibility of producing methane from fruit and vegetable waste (FVW) was performed in two different stages: an initial stage with different conditions for high biogas and methane yields and VS removal evaluated in batch experiments. The evaluation

of the anaerobic digestion process in a fed-batch mode and the feasibility of the long operation time under stable conditions were determined in a second stage of the project.

The design and efficient operation of an anaerobic digestion system can be determined by establishing the physical and chemical characteristics of the organic waste and the culture conditions, which have an effect on biogas production and process stability of the system. The residue mixture used as feedstock was composed of products most frequently and consistently sold in the market (i. e., excluding seasonal products). The FVW mixture (equal proportions of each residue, w/w) showed a total solid (TS) content of approximately 73-100 g/Kg waste (approximately 10%), a pH of 4, and a moisture content of 90% (Garcia-Pena et al., 2011). The FVW had a higher soluble carbohydrate content (only contained fruits and vegetables and did not include a source of protein), a high moisture content, and could be considered a highly degradable substrate. These properties make it an ideal candidate for CH4 production.

Since the FVW is highly degradable, large amounts of volatile fatty acids (VFA) are produced and a rapid acidification of the system could inhibit the biological activity of the methanogens. Some reports have demonstrated that pH control is one of the most important parameters in achieving high biogas production (Mata-Alvarez 1992, Bouallagui et al., 2005). Additionally, as mentioned above, the FVW contains no nitrogen source. Some experiments were also performed to evaluate the effect of adding a nitrogen source, considering that an adequate C/N ratio is necessary to enhance the anaerobic digestion process. Different conditions were thus tested to optimize biogas and methane production using FVW, including buffered and nitrogen supplemented systems with and without inoculation.

Figure 1 shows the data obtained for TS removal, biogas production (m3/kgVS) and final pH under the evaluated conditions. As an overall result, the inoculation, pH control and nitrogen source addition all had positive effects on VS reduction and biogas yield. Higher degradation percentages of approximately 86 % of the initial total volatile solid (tVS) were obtained in the inoculated and pH-regulated system (IpH) as well as in the inoculated, pH — regulated and nitrogen-added system (IpHN) in a 28-day culture. Higher VS removal was correlated with higher biogas production. The highest biogas production (0.42 m3/kgVS) was obtained in the inoculated system with pH control and nitrogen addition (IpHN), reaching a VS removal percentage of 86%.

Lower biogas productions of 0.15 m3/kgVS and 0.08 m3/kgVS were measured in the systems without inoculum (WIpH and WIpHN) and had correspondingly low VS removals of 42 and 34%, respectively.

The results suggested a correlation of pH with biogas productivity, with higher productivity occurring at pH values close to the optimum pH of 7. Methane production (approximately 45-53+0.5% v/ v in the biogas mixture) only occurred in the inoculated systems, with the highest methane percentage (53 %, v/ v) observed for the IpHN system.

Biogas and CH4 production were in the range (0.16-0.47 m3/kgVS) of those reported by other authors for anaerobic digestion processes using FVW as a feedstock (Rajeshwari et al., 1998, Alvarez 2004, Mata-Alvarez et al., 1992; Boullagui et al., 2003). In the inoculated systems, both nitrogen addition and pH control had positive influences on biogas production. Therefore, these conditions should be used to produce the maximum amount of methane from FVW.

System

Fig. 1. VS removal percentage (%/100); Biogas productivity in m3/kgVS; (O) Final pH obtained for different conditions evaluated in the batch systems. I, FVW inoculated with cow manure (10%); IN, FVW inoculated and supplemented with NHCl as a nitrogen source; IpH FVW inoculated and salts added (buffer) to control pH; IpHN, FVW inoculated, buffering salts, and NH4Cl added; WI, FVW without inoculation (Control); WIN, FVW and NH4Cl; WIpH, FVW and buffering salts; and WIpHN, FVW buffering salts and NH4. Modified from Garcia-Pena et al., 2011.

Similar conditions were obtained by the codigestion of a mixture of FVW and meat residues (obtained from meat packaging operations at the same market). The meat residues (MR) provide a high nitrogen concentration, and protein hydrolysis could result in natural pH control due to NH4 production. For the codigestion system of FVW and MR, the highest biogas yield of 0.9 m3/kgVS (methane yield of 0.45 m3/KgVS) was observed, reaching an organic matter degradation of 93% (Figure 1).

The feasibility of an anaerobic digestion process using FVW and MR was then evaluated in a 30 L ADR system. To determine the effect of MR addition on biogas and methane production, experiments were carried out using different MR proportions. The biogas productivity and methane percentages obtained under different conditions after 130 days of operation are presented in Table 1.

In the first stage, no methane was observed in the biogas effluent, thus biogas production resulted from the hydrolysis of the easily degradable components of the feedstock. After 20 days of operation, the anaerobic digestion reactor (ADR) was inoculated with (13 %, v/ v cow manure) and a new, strong biological activity was observed. In this period, the CH4 content in the biogas was 16 % (v/ v) due to the initial activity of the methanogenic population introduced into the ADR with the inoculum. The methane percentage increased from 16 to 30% (v/ v) as the proportion of MR (50:50) increased. When steady state was reached (after 80 days of operation) with a 75:25 mixture of FVW and MR, the CH4 percentage was stable at 53 ± 2 %, and the pH was stable at 6.9 ± 0.5 (naturally regulated during this last stage of the process).

For the next stage (on the 70th day of operation), a 50:50 mixture of FVW:MR was added and the CH4 percentage recovered to 30%. Once stable operation was achieved after 83 days, the biogas production showed a constant value of approximately 0.25 m3/kgVS and a methane percentage of 53%, corresponding to a methane production of 0.135 m3/kgVS and a VS removal of 78%. The reactor was regularly fed with a 75:25 mixture of FVW:MR. Under these conditions, the CH4 percentage was stable at 53 ± 2 %, and the pH was stable at 6.9 ± 0.5.

An appropriate buffering capacity and a highly stable experimental system were observed with Organic Loading Rates (OLRs) in the range of 2.4 to 2.7 g COD/L day (Hydraulic Retention Times (HRT) in the range of 15-20 days). The natural pH regulation during the stable operation of the ADS was a result of NH3 release from protein hydrolysis. The results could also be explained as an effect of the alkalinity in the system. At normal percentages of CO2 in the digester gas, between 25 and 45%, a total alkalinity of at least 500 to 900 mg/L is required to keep the pH above 6.5. Higher CO2 partial pressure makes alkalinity requirements larger (Rittmann and McCarty, 2001). When the meat residues were introduced into the ADS, the alkalinity started to increase considering that the moles of bicarbonate alkalinity was equal to the moles of NH4 according to the stoichiometric equation for methanogenesis of an organic mixture (carbohydrates and proteins) (Garcia — Pena et al 2011). Additionally, at stable and at long operation times the CO2 percentage was lower than those obtained during the start-up of the ADS. The required alkalinity was 3445 mg/L, while an alkalinity as CaCO3 of 4804.6 mg/L was calculated under the experimental conditions (i. e., 70% removal efficiency and an initial substrate concentration of 50 gCOD) using the stoichiometric equation for an organic mixture of carbohydrates and protein (50:50) (Garcia-Pena et al, 2011). This total alkalinity value was high enough to avoid a possible acidification of the Anaerobic Digestion System (ADS), and the high buffering capacity allowed stable operation without external control. The increase in methane production after the 80th day of operation could have resulted from an increase in the methanogenic population and its adaptation to the operating conditions of the ADS. The high VS removal, the increased methane yield, and the natural pH control during the stable period of the ADS was due to an adequate ratio of nutrients and the availability of proteins for new cell synthesis (Garcia-Pena et al 2011).

The accumulation of the volatile fatty acids (VFA) during the non balance of the process reflects directly an uncoupling kinetic between the acid producers and consumers (Hickey & al., 1989). The concentration of VFA was suggested for the control and the monitoring of the anaerobic digester (Hill & Bolte, 1989). The VFA is generally measured by gas chromatography (GC) with the use of a detector with ionization of flame (FID), to obtain the individual VFA, or by titration which gives the concentration of total VFA, and which is less expensive and is largely used at the commercial biogas plants. Several methods of titration for the determination of total VFA were proposed, for example a simple titration (Delbes, 2000), a titration at 5-point, and a titration at 8-point.

However, several studies specified that the individual VFA can provide more significant information concerning an early failure of the process the failure of process (Nielsen, 2006).

Nowadays, an excessive use of fossil fuels has led to significant emissions of CO2 in the atmosphere which is responsible for causing extensive climate changes (Soccol et al., 2010). As a result of this with the increase in fossil fuel prices direct the efforts towards utilizing renewable energy sources. Considerable progress in searching for alternative energy sources has been made since the oil crisis of 1973. However, it must be noted that an only the renewable biomass used for energy production contributes to the reduction of negative environmental impacts, e. g. decreased GHG emissions.

Currently, commercial biofuels production, such as ethanol and biogas, relies mostly on the fermentation of cane sugar, molasses or glucose derived from corn, sugar beet, wheat or potatoes. It is not economically accepted because these biomass production for biofuels competes for the limited agricultural land needed for food and feed production. Much of the hydrogen produced in the world is obtained from natural gas, which is not environmental friendly. Therefore, a significant increase in biofuels production would be possible only if technologies are developed to convert the waste biomass.

Dairy industry, like most other food industries, generates strong wastewaters characterized by high COD concentrations representing their high organic content (Demirel et al., 2005). Whey is by-product of milk processing and is abundantly obtained during cheese production. According to Najafpour et al. (2008), worldwide cheese production generates more than 145 million tonnes of liquid whey per year. In the case of deproteination of whey for the production of a valuable human food additive, the residual whey permeate is still a waste with high COD and must be treated before disposal. Due to its lactose major component, whey permeate is a well defined and suitable substrate for anaerobic digestion (Kourkoutas et al., 2002; Najafpour et al., 2008; Venetsaneas et al., 2009; Zafar & Owais, 2006). UF whey permeate fermentation in UASB reactors to produce biofuels (bioethanol, biogas, biohydrogen) has been successfully tested in this study.

5. Acknowledgements

The study of bioethanol production was supported by a grant N523 049 32/1753 from Ministry of Science and Higher Education, Poland in 2007 — 2008.

The study of biohydrogen production was supported by a grant N N 523 555138 from Ministry of Science and Higher Education, Poland in 2010 — 2013.

In order to test the performance differences among the three kinds of biogas residue fibre mulch, black biodegradable mulching added in activated carbon, plastic film and control (without mulching), to cultivate eggplant, a comparative field test through the multiple comparisons for the soil moisture content, soil temperature, weed growth amount and eggplant yield was employed. Performance index of the treatments was shown in table4- 1.

4.1
Effect of different treatments on the weed amount

The effect scene of different treatments on the weed amount in the case of cultivating eggplant was shown in Fig.4-1. Weed amount of mulching was markedly less than the control, and weed amount of plastic film was more than biogas residue films. In the period of observation, weeds were flourished under the plastic film or even broke plastic mulch. Weeds mainly grew from transplanted hole and rupture to all the treatments, and making the film rupture expands.

Fig. 4-1. The effect scene of different treatments on the weed amount in the case of cultivating eggplant

The measured results of total weeds of each treatment were shown in table 4-2.

There were significant differences among the treatments, according to analysis of the multiple comparisons among treatments, seeing table 4-4.

Mean difference (g)

LSD

The results showed that there were significant differences between three kinds of biogas residue fibre film, black film and plastic film, control; there were significant differences between three kinds of biogas residue fibre films and black film. Weed amount of A biogas residue fibre film decreased 81% as compared with control, and decreased 75% as compared with the plastic film; weed amount of B biogas residue fibre film decreased 82% as
compared with control, and decreased 77% as compared with the plastic film; weed growth amount of C biogas residue fibre film decreased 84% as compared with control, and decreased 79%as compared with the plastic film. From this, three kinds of residue fibre films had significant effect of suppressing weeds.