Water hyacinths as a resource in agriculture and energy production: a literature review

Water hyacinths are becoming a problem in lakes, ponds and waterways in many parts of the world. This paper contains a literature study of different ways to use water hyacinths, mainly in agricultural or alternative energy systems. The literature review indicated that water hyacinths can be rich in nitrogen, up to 3.2% of DM and have a C/N ratio around 15. The water hyacinth can be used as a substrate for compost or biogas production. The sludge from the biogas process contains almost all of the nutrients of the substrate and can be used as a fertiliser. The use of water hyacinth compost on different crops has resulted in improved yields. The high protein content makes the water hyacinth possible to use as fodder for cows, goats, sheep and chickens. Water hyacinth, due to its abundant growth and high concentrations of nutrients, has a great potential as fertiliser for the nutrient deficient soils of Africa and as feed for livestock. Applying the water hyacinths directly without any other processing than sun drying, seems to be the best alternative in small-scale use due to the relatively small losses of nutrients and workload required. To meet the ever-growing energy demand, biogas production could be one option but it requires investments and technological skills that would impose great problems in developing countries where the water hyacinth is often found. Composting as an alternative treatment has the advantage of a product that is easy to work into the soil compared with dried water hyacinths, because of the decomposed structure. Harvesting and transport of water hyacinths can be conducted manually on a small scale and does not require a new harvesting technique to be introduced. Transporting of fresh water hyacinths means, if used as fertiliser in amounts large enough to enhance or effect crop growth, an unreasonably large labour requirement. Based on the labour need and the limited access to technology, using dried water hyacinths, as green manure is a feasible alternative in many developing countries.     

Control of GHG emission at the microbial community level

All organic material eventually is decomposed by microorganisms, and considerable amounts of C and N end up as gaseous metabolites. The emissions of greenhouse relevant gases like carbon dioxide, methane and nitrous oxides largely depend on physico-chemical conditions like substrate quality or the redox potential of the habitat. Manipulating these conditions has a great potential for reducing greenhouse gas emissions. Such options are known from farm and waste management, as well as from wastewater treatment. In this paper examples are given how greenhouse gas production might be reduced by regulating microbial processes. Biogas production from manure, organic wastes, and landfills are given as examples how methanisation may be used to save fossil fuel. Methane oxidation, on the other hand, might alleviate the problem of methane already produced, or the conversion of aerobic wastewater treatment to anaerobic nitrogen elimination through the anaerobic ammonium oxidation process might reduce N2O release to the atmosphere. Changing the diet of ruminants, altering soil water potentials or a change of waste collection systems are other measures that affect microbial activities and that might contribute to a reduction of carbon dioxide equivalents being emitted to the atmosphere.     

Effect of C/N on composting of pig manure with sawdust

The aim of this composting trial was to evaluate the effect of C/N on the composting process of pig manure with the purpose of reducing the amount of sawdust normally used as co-composting materials. Two aerobic static piles were prepared consisting of pig manure mixed with sawdust at an initial C/N of 30 (pile A) and 15 (pile B), respectively. Pile B containing larger amount of pig manure showed a slower rise in temperature, lower maximum temperature, and shorter thermophilic phase than pile A. It also resulted in higher pH and electrical conductivity (EC) values, and even higher contents of soluble NH4-N and volatile solids throughout the composting period. Chemical and biological parameters including dissolved organic carbon (DOC) (4932 mg kg(-1)), soluble NH4-N (371 mg kg(-1)), C/Nsolid (18.3), C/Naquoeus (5.8) and seed germination index (GI) (66.5%) indicated that pile A achieved maturity after 49 days of composting. After 63 days of composting, pile B contained 5352 and 912 mg kg(-1) of DOC and soluble NH4-N content, respectively, which was much higher than the criterion of 5% and 400 mg kg(-1), indicating its immature nature. Pile B showed a relatively low GI value of 46%, which may be due to its high indigenous EC value as a result of larger amount of pig manure. Therefore, co-composting of pig manure with sawdust at a low initial C/N would require a composting longer than 63 days, and, the high salinity due to the large amount of pig manure would pose a potential inhibition on plant growth.     

Anaerobic biogasification of undiluted dairy manure in leaching bed reactors

Dry anaerobic digestion of high solids animal manure is of increasing importance since conventional slurry digestion is not an effective system for these manures. The investment costs for large-size reactors, costs for heating these reactors, handling, dewatering, and the disposal of the digested residue decrease the benefits of conventional slurry anaerobic digestion for high solids animal manure. Even though leaching bed reactors (LBR) constitute a promising option for dry anaerobic biogasification of animal manure, no study is cited in the literature for animal manure, excluding a single study on cattle waste which utilized a similar concept in a different experimental set-up, namely a packed bed digester. Therefore, this work was undertaken to investigate the anaerobic biogasification of undiluted dairy manure in LBRs. To this purpose anaerobic leaching bed reactors (ALBR) packed with a mixture of dairy manure, anaerobic seed and wood powder/chips were operated. The ALBRs were fed with water, and the leachate that was collected from their effluents was subjected to biochemical methane potential (BMP) experiments to determine the biogas production. The results revealed that LBRs can successfully be applied to anaerobic digestion of undiluted dairy manure with around 25% improvement in biogas production relative to conventional (slurry) anaerobic digesters.     

养猪业清洁生产途径与循环经济发展模式探讨

近年来,我国养猪业发展迅速,农村经济增长较快,农民收入和生活水平明显提高。同时,养猪业产生的猪粪便污染日趋严重,已严重影响当地居民生产生活和身体健康。为了彻底消除农村养猪场猪粪便污水和臭味污染,改善农村环境质量,促进农业经济发展,总结了长期从事清洁生产和循环经济发展研究的实践经验,提出了养猪业清洁生产途径和循环经济发展模式,意在从源头预防控制污染,大力推进养猪业清洁生产与农村经济可循环持续发展,并供关心我国养猪清洁生产与循环经济发展的同行借鉴参考。     

Development of nutrient cycle through agricultural activities of a rural area in the North of Vietnam

Material flow analysis (MFA) has been applied to assess the environmental impact of human activities on nutrient flows at the commune scale. This paper reports the assessment of human excreta and animal manure as a nutrient source for paddy fields and fishponds in Hoang Tay commune, Ha Nam province, Vietnam. The quality of MFA model was confirmed through modified uncertainty analysis, then was used to originally quantify and visualize the interlinks of livestock with the environmental sanitation and agricultural system in terms of nutrients. Currently, half of the pig manure was collected to the biogas, and the remainders were freely discharged to the commune’s drainage system (25%) or directly reused in the paddy fields (25%). While wastewater in the drainage system was the biggest source of nitrogen (contributed 46%), paddy field was the biggest source of phosphorous (contributed 55%) discharged to the Nhue River, totaling 57 ± 9 ton N and 29 ± 6 ton P, annually. Consequently, mitigation measures for nutrient resource management were proposed, and reducing half of chemical fertilizers applied and reusing all excreta and manure in the paddy fields were the most effective option.     

Bioconversion of dairy manure by black soldier fly (Diptera: Stratiomyidae) for biodiesel and sugar production

Modern dairies cause the accumulation of considerable quantity of dairy manure which is a potential hazard to the environment. Dairy manure can also act as a principal larval resource for many insects such as the black soldier fly, Hermetia illucens. The black soldier fly larvae (BSFL) are considered as a new biotechnology to convert dairy manure into biodiesel and sugar. BSFL are a common colonizer of large variety of decomposing organic material in temperate and tropical areas. Adults do not need to be fed, except to take water, and acquired enough nutrition during larval development for reproduction. Dairy manure treated by BSFL is an economical way in animal facilities. Grease could be extracted from BSFL by petroleum ether, and then be treated with a two-step method to produce biodiesel. The digested dairy manure was hydrolyzed into sugar. In this study, approximately 1248.6 g fresh dairy manure was converted into 273.4 g dry residue by 1200 BSFL in 21 days. Approximately 15.8 g of biodiesel was gained from 70.8 g dry BSFL, and 96.2 g sugar was obtained from the digested dairy manure. The residual dry BSFL after grease extraction can be used as protein feedstuff.     

Petroliferous wastewaters treatment with water hyacinths (Raffinerie de Provence, France): Experimental statement

The production and purification abilities of the water hyacinth, Eichhornia crassipes (Mart.) Solms., were tested on petrochemical wastewaters at Raffinerie de Provence, Total (La Mède, France), in controlled and in situ experiments. The mean production obtained was of about 6.1 g (dry weight) day⁻¹ m⁻² (10-fold lower than those obtained on paper industry effluent), and can be explained by the high salinity and pH of the effluent, and the negative effect of hydrocarbons. In comparison with the control pond, the water hyacinth system induced a rapid settlement effect. Finally, the removal gains due to the water hyacinths system were about 26% for the suspended solids (i.e. 40.1 kg day⁻¹), 28% for the total hydrocarbons (i.e. 17.2 kg day⁻¹) and 18% for the total organic carbon (i.e. 27 kg day⁻¹).     

Effects of commercial bacterial products on nutrient transformations of pig manure in a pig-on-litter system

A preliminary study was carried out in an experimental farm in Hong Kong to investigate the changes in microbial populations and nutrient concentrations of a pig waste mixture during a 10-week in-situ decomposition of pig manure in a pig-on-litter system. The effects of two commercially available bacterial products on this decomposition process were also examined. The results show that both heterotrophs and nitrifiers increased their populations to 10¹⁵ MPN (Most Probable Number) g⁻¹ waste mixture at the end of the 10-week study while the denitrifiers varied around 10¹⁰ MPN g⁻¹ during the period of investigation. By contrast, the fungal Colony Forming Units (CFU) declined rapidly within the first week and remained at 105 CFU g⁻¹ waste mixture throughout the rest of the study period. There was no accumulation of inorganic N in the pig waste mixture. The offensive odour of NH, was not detected in the pig pens. The C:N ratios of the waste mixture gradually declined reaching a final value of 22:1. The concentration of total Kjeldahl N, phosphorus and potassium in the final product were significantly higher when compared with the initial phase of the study. These findings suggest that a part of the organic nutrients released from the pig manure might have been mineralized and assimilated into microbial biomass similar to compost. In general, the nutrient concentrations of the two pig waste mixtures treated by two different bacterial products were similar. This indicates that the effects of these two products on the in-situ decomposition of pig manure were fairly similar. A control pen without the addition of bacterial products became foul within one week and had to be abandoned.     

Salinity, organic content, micronutrients and heavy metals in pig slurries from South-eastern Spain

The increase in commercial pig production is an opportunity to reuse animal manures in arid and semiarid soils as a source of nutrients and organic matter. However, there are components in pig slurry that are potentially dangerous for the environment. In this study, pig slurries of 36 pig farms in South-eastern Spain were evaluated for salt content (electrical conductivity, chloride and sodium), organic load (BOD5 and COD), micronutrients (Fe, Cu, Mn and Zn), and heavy metals (Cd, Co, Cr, Ni and Pb). Except for electrical conductivity, Cu and Zn, components in pig slurries did not vary considerably between animal production stages, indicating similar management of diverse animal types. Assuming an application rate based on the maximum input of nitrogen from animal manure (210 kg total N/ha/yr), the estimates for soil annual load of Cl and Na, 415 kg/ha, could be a significant salinisation risk. Cu and Zn seemed to be the metals that could be accumulated most in soils where application of pig slurries is common (4 and 15 kg/ha/yr, respectively). The estimated heavy metal (Cd, Co, Cr, Ni and Pb) input to soils would be 260 g/ha/yr, with a relative contribution of Cr>Ni>Pb>Co>Cd.     

Short term effects of copper, sulfadiazine and difloxacin on the anaerobic digestion of pig manure at low organic loading rates

Antibiotics of inorganic and organic origin in pig manure can inhibit the anaerobic process in biogas plants. The influence of three frequently used antibiotics, copper dosed as CuSO₄, sulfadiazine (SDZ), and difloxacin (DIF), on the anaerobic digestion process of pig manure was studied in semi-continuous experiments. Biogas production recovered after every Cu dosage up to a sum of 12.94 g Cu kg⁻¹ organic dry matter (ODM), probably due to Cu precipitation following the formation of sulphide from sulphate. Complete inhibition was found at the very high Cu concentration of 19.40 g Cu kg⁻¹ ODM. Inhibitory effect of SDZ and DIF was observed at concentrations as high as 2.70 g kg⁻¹ ODM and 0.54 g kg⁻¹ ODM, respectively. It seems very unlikely that the antibiotics tested would inhibit the anaerobic process in a full-scale biogas plant.     

Agricultural reuse of the digestate from low-cost tubular digesters in rural Andean communities

This research aimed at assessing the properties of guinea pig manure digestate from low-cost tubular digesters for crops fertilization in rural Andean communities. To this end, field trials were carried out to evaluate the effect of the digestate on two common Andean crops: potato (Solanum tuberosum) and forage (Lolium multiflorum and Trifolium pratense L.). The potato yield (20-25 tha(-1)) increased by 27.5% with digestate, by 15.1% with pre-compost and by 10.3% with the mixture, compared to the control. The forage yield (20-21 tha(-1)) increased by 1.4% with digestate - 50% dose, and by 8.8% with digestate - 100% dose and digestate - 150% dose, compared to the control. The results suggest that the digestate is an appropriate substitute of manure pre-compost for potato fertilization. The results with forage indicate that it can be applied in a range of doses, according to the amount produced by the digester. Currently, manure is either used for cooking or as fertilizer. With low-cost tubular digesters implementation, it could be used to feed the digester, using the digestate for crops fertilization and biogas for cooking; improving household living conditions and protecting the environment. Since soil properties in rural Andean communities differ from experimental layouts, the effect of fertilizers should be re-evaluated in-situ in future research studies.     

Co-digestion of cattle manure with food waste and sludge to increase biogas production

Anaerobic co-digestion strategies are needed to enhance biogas production, especially when treating certain residues such as cattle/pig manure. This paper presents a study of co-digestion of cattle manure with food waste and sewage sludge. With the aim of maximising biogas yields, a series of experiments were carried out under mesophilic and thermophilic conditions using continuously stirred-tank reactors, operating at different hydraulic residence times. Pretreatment with ultrasound was also applied to compare the results with those obtained with non-pretreated waste. Specific methane production decreases when increasing the OLR and decreasing HRT. The maximum value obtained was 603 LCH(4)/kg VS(feed) for the co-digestion of a mixture of 70% manure, 20% food waste and 10% sewage sludge (total solid concentration around 4%) at 36°C, for an OLR of 1.2g VS/Lday. Increasing the OLR to 1.5g VS/Lday led to a decrease of around 20-28% in SMP. Lower methane yields were obtained when operating at 55°C. The increase in methane production when applying ultrasound to the feed mixtures does not compensate for the energy spent in this pretreatment.     

An international study: Effect of farm manure on the release of phosphorus from fly ash

Fly ash is abundantly produced from thermal power plants and is considered a hazardous waste. However, in recent years, fly ash has been widely utilized in the agricultural sector as a soil modifier. It is particularly important for wasteland/mine spoil reclamation due to its ability to provide a source of plant nutrients and improve physicochemical properties of soil. Although fly ash itself contains many plant nutrients, most nutrients, including phosphorus (P), are in a bound form not easily available to plants. This study analyzed the effect of farm manure on the solubility of P from fly ash. Incubation studies were conducted to determine the effect of farm manure on P solubilization to use as a potential option for remediation. © 2007 Wiley Periodicals, Inc.     

Solid recovery rate of food waste recycling in South Korea

Source-separated collection system of household food waste has been implemented national wide in South Korea. Food waste recycling rate that means conversion rate to recycle is over 90 % in present. However, over the value of 90 %, we need to enhance the efficiency of food waste recycling process. We analyzed material flow of 24 food waste recycling facilities and calculated solid recovery rate to key-process. We found that 3–13 % of the solids from food waste outflows with foreign materials and 27–33 % of the solids outflow with wastewater. As a result, solid recovery rates are 65.3, 60.9, and 56.3 % in wet feed facility, dry feed facility, and composting facility, respectively. Alternative ways to recovery solid from wastewater or collection tools to exclude plastic bags, salt, and moisture content are required to make food waste recycling more efficient.     

Aqueous leaching of cattle manure incineration ash to produce a phosphate enriched fertilizer

Ash produced from the combustion of livestock manure contains large amounts of phosphorus (P), which is an important resource as a fertilizer. Some studies have extracted and recovered P from incinerated biomass ash using inorganic acid or alkaline agents, which produce wastewater that requires treatment and is expensive due to the cost of chemicals. Livestock manure ash contains not only P, but also water soluble salts, which could be a negative influence on plant growth and shall be preferably removed from the recovered fertilizer. In this study, we removed salinity from cattle manure incineration ash by simple aqueous leaching, while retaining the P content. The optimal condition was a 20 min leaching time at a liquid/solid (L/S) ratio of 10 mL g-ash^?1. Under this condition, over 90 % of Cl and 20 % of Na in the original ash was removed, while over 99 % of the P was retained in the leached residue. The leached residue met the fertilizer standard in Japan in terms of citrate soluble fertilizer components and contained few heavy metals. X-ray analyses of the ash indicated that Cl was mainly present as KCl in the original ash, while P was mainly present as Ca compounds in the ash.     

Poly(vinyl alcohol)/Compost Composites for Biofiltration of Swine Waste Volatiles

In this study, a Poly(vinyl alcohol)(PVA)/compost composite bead is prepared and is indicated suitable as a filter material for biofiltration. The optimal preparation process is with the compost size of 16–35 mesh, the ratio of water to compost of 40 g/15 g compost, and the immersion time in the phosphate solution of 60 min. The composite bead prepared by this process is a porous spherical particle with a diameter between 2.4 and 6.0 mm and a density of 0.96 g/cm³. It contains 9.43 mg P/g dry solid and 12.1 mg N/g dry solid. The equilibrium moisture content of the composite bead bed from adsorption and holding experiments is 50.5 and 54.6% on a wet basis respectively, which is about 1.74 times higher than that of swine manure compost bed. It corresponds to the optimal filter material required and is sufficient to sustain biological activity as the composite bead adsorbs equilibrium moisture. The bulk compressive strength of the composite bead bed is about 1.15 times larger than that of swine manure compost bed to ensure even distribution of air flow and reduce the head loss as the air flow stream passed through. The pH value of the filter bed could maintain in the 6.9–7.2 range during the operation period due to the composite bead has the phosphate buffer capacity. The percentage of ethyl acetate removal could remain at over 99% for 40 days operation while the composite beads adsorbed inorganic nitrate nutrients. The pressure drop of two kind composite beads and pig manure compost filter beds are 0 and 2 mm H₂O, respectively, after operating for 40 days.     

Greenhouse gas emission reduction and environmental quality improvement from implementation of aerobic waste treatment systems in swine farms

Trading of greenhouse gas (GHG) emission reductions is an attractive approach to help producers implement cleaner treatment technologies to replace current anaerobic lagoons. Our objectives were to estimate greenhouse gas (GHG) emission reductions from implementation of aerobic technology in USA swine farms. Emission reductions were calculated using the approved United Nations framework convention on climate change (UNFCCC) methodology in conjunction with monitoring information collected during full-scale demonstration of the new treatment system in a 4360-head swine operation in North Carolina (USA). Emission sources for the project and baseline manure management system were methane (CH4) emissions from the decomposition of manure under anaerobic conditions and nitrous oxide (N2O) emissions during storage and handling of manure in the manure management system. Emission reductions resulted from the difference between total project and baseline emissions. The project activity included an on-farm wastewater treatment system consisting of liquid-solid separation, treatment of the separated liquid using aerobic biological N removal, chemical disinfection and soluble P removal using lime. The project activity was completed with a centralized facility that used aerobic composting to process the separated solids. Replacement of the lagoon technology with the cleaner aerobic technology reduced GHG emissions 96.9%, from 4972 tonnes of carbon dioxide equivalents (CO2-eq) to 153 tonnes CO2-eq/year. Total net emission reductions by the project activity in the 4360-head finishing operation were 4776.6 tonnes CO2-eq per year or 1.10 tonnes CO2-eq/head per year. The dollar value from implementation of this project in this swine farm was US$19,106/year using current Chicago Climate Exchange trading values of US$4/t CO2. This translates into a direct economic benefit to the producer of US$1.75 per finished pig. Thus, GHG emission reductions and credits can help compensate for the higher installation cost of cleaner aerobic technologies and facilitate producer adoption of environmentally superior technologies to replace current anaerobic lagoons in the USA.     

Low energy comsumption management of agricultural residues

In this paper, a mechanical filtering system to treat pig slurry is proposed. The filter was made from the aerobic decomposition product of the organic fraction of municipal wastes and wheat straw was used as the support.Using a pilot plant to treat 2100 liters of swine slurry, an adequate reduction in BOD₅; COD, and other parameters was obtained. The organic matter content of the material trapped in the filter was similar to that of compost and farmyard manure, but the nitrogen and phosphorous levels and the C/N ratio were more similar to farmyard manure. After passing through a filtering system, the treated liquid can be used for fertirrigation and as a feed for algae ponds. After a period of stabilization, the solid material can be mixed to produce manure. Although wheat straw was used as the support in this experiment, other agricultural wastes such as rice straw, corn stalks, millet stems, banana, cotton, and coconut trash can be used. Rather than municipal solid waste compost, other kinds of compost obtained from agricultural wastes such as leaves, bark, husks, etc., can be used as the filter.     

Pilot project of biogas production from pig manure and urine mixture at ambient temperature in Ventanilla (Lima, Peru)

Parque Porcino de Ventanilla has an extension of 840ha with 2200 farmers dedicated to pig production. There is a lack of services in the area (i.e., water supply, electricity, or waste collection). Anaerobic treatment of pig manure would replace current dumping and incineration, reducing environmental pollution and hazards to public health, as well as providing an organic fertilizer and biogas. The objective of the present work was to study the viability of ambient temperature anaerobic digestion of pig manure diluted in urine, by means of on-site pilot scale reactors. The final goal was to establish design parameters for anaerobic digesters to be implemented; since it was part of a project to improve life conditions for the farmers through the incorporation of better management techniques. Experiments were carried out in a low-cost pilot plant, which consists of three anaerobic digesters (225L total volume), without heating or agitation, placed in a greenhouse. The start-up of the digestion process was performed with a mixture of temperature adapted pig manure-sludge and fresh rumen, and showed a good performance regardless of the dilution of pig manure with water or urine, which is a key parameter due to the scarcity of water in the area under study.