REVISTA AIDIS Investigación, desarrollo y práctica. WATER HYACINTH COMPOSTING AS A WASTE MANAGEMENT STRATEGY: A SYSTEMATIC REVIEW

Macrophytes proliferation problem is worldwide know resulting in impacts on natural environment, human health and economic activities. These organisms have several parameters resilience, which ensures high rate of reproduction and proliferation, hindering their management. As a management difficulty consequence, however, solutions are sought to disposal this large amount of macrophytes, such as composting and fertilizer production. Thus, this study aims to conduct a systematic literature review in Scientific Platforms Science Direct and Scopus, identifying current status of macrophytes composting process, main methods, analyses and results obtained, in order to contribute in innovation studies to convert this type of weed into fertilizer. The general words source in titles, summary, or keywords specified by author were “Macrophyte” or “water hyacinth” and “compost” or “composting”. Only articles dating from the last 20 years were maintained. Macrophyte composting process interest is addressed around the world because of their potential environmental, economic and social impacts, mainly for Eichhornia crassipes. Natural aeration predominates (56%) with composting time equal to or less than 60 days. Humidity control is essential (around 60%) like macrophytes dehydration prior to the composting process beginning. The significant quantity cellulose requires previous comminution and/or the cellulose‐degrading inoculants addition. Composting process operational parameters are not standardized. Micro and macro nutrients richness can be considered for next evolutionary composting studies stage for this plant type, either by organic matter sources characteristics and/or mineral sources addition.


Introduction
The natural environment, economic activities and human health have been impacted by the proliferation of macrophytes. Biological factors of reproduction and development for these species are extremely relevant to the difficulties encountered in its management. The excessive availability of nutrients, such as Nitrogen (N), Phosphorus (P) and Potassium (K), usually associated with human activity, contribute to the formation of macrophytes floating mats (Sharma et al., 2016;Bote et al, 2020). These organisms withstand saline conditions (≤10 ppt), wide temperature range (from 1 to 40 °C) and pH (from 4 to 8) (Wilson et al., 2005;Sharma et al., 2016).
Macrophytes contain, on average, more than 95% water (Malik, 2007;Rezania et al., 2015a), long and hanging roots from 0.4 to 1 meters. Vegetation reproduction is asexual and its seeds remain dormant for long years (Malik, 2007;Bote et al., 2020). Its proliferation can also occur from fragments of its stems (Gunnarsson and Petersen, 2007). The mass productivity of macrophytes which can vary from approximately 140 tons/ha per year (Gunnarsson and Petersen, 2007) to 400 tons, with a density of 50 to 60 kg/m² (Malik, 2007;Rezania et al., 2015a).
Macrophytes have an excellent capacity to absorb nutrients and other chemicals from the environment. Ganesh et al. (2012), Singh and Kalamdhad (2012), Singh and Kalamdhad (2014) and Mazumder et al. (2020) show the elements presence such as Chromium (Cr), Cadmium (Cd), Lead (Pb), and Mercury (Hg) in macrophyte chemical analyzes.
The proliferation of macrophytes in water bodies, however, results in impacts on the natural environment, human health and economic activities. The green mats formation on water contributes to increase of water loss due evapotranspiration (Bote et al., 2020), decrease light penetration into the water (Malik, 2007), decreasing the productivity of phytoplankton (Sharma et al., 2016), and can increase decomposing of submerged vegetation reducing oxygen content (Bote et al., 2020), as a consequence decreasing fish habitat quality and the aquatic environment eutrophication. Gunnarsson and Petersen (2007) and Sharma et al. (2016) refer to studies that correlate macrophytes excessive accumulation in water bodies with formation of real breeding grounds for vector organisms, and diseases such as malaria. Malik (2007) also presents examples of regions around the world where macrophyte infestations have become vectors disease source.
Thus, the management (proactive or reactive) of this plant type have fundamental importance, given potential impacts. Adopted management practices, regardless, for water resources where macrophytes are a reality, the final destination must be considered in the adopted action plan. Due to its fibrous tissue and its high energy and protein content, useful macrophytes applications have already been described by some authors, such as (Gunnarsson and Petersen, 2007), Malik (2007) and Rezania et al. (2015a) and Rezania et al. (2015b), including composting.
Thus, the study objective is realize a structured review of the literature on Scientifics platforms Science Direct and Scopus, in order to identify the macrophyte composting process status, main methods, analyzes and results obtained, in order to contribute to the continuity innovation in studies of converting this plant type into fertilizer.

Methodology
Research structure was defined for access and identification, on scientific platforms, of scientific researches on composting macrophytes, as described below.

Systematic review
Studies identification in scientific journals was performed by a systematic search on the Science Direct and Scopus platforms. The general source of words in the title, abstract or keywords specified by the author were "Macrophyte" or "water hyacinth" and "compost" or "composting". An additional screening was realized in order to maintain only scientific researches in which composting practices were applied in/with macrophyte species. In this systematic review, only English literature reported was included in the scope of the review and only research articles were selected. Articles dated with more than 20 years old, that is, the date prior to the year 2000, were disregarded. Table 1 shows the classification criteria of the articles identified in systematic literature review.

Results
Initially 125 scientific articles were identified. Figure 1 illustrates the result of the performed research on the scientific platforms. After applying the additional screening criteria specified in methodology, 88 scientific articles were maintained in the literature review. The largest fraction of these articles (63) were identified on Scopus Platform, followed by articles available in both platforms (23) and articles available only on the Science Direct Platform (2).    Main macrophtes composting methods Goyal et al. (2005), Martins et al (2019) and Bui et al. (2015) used static cells for biomass composting, to produced organic fertilizer as objective. Although they realized a study in distinct locations (India and Brazil, respectively) and differed in the sources of biomass (only macrophytes; macrophytes, pruning, seeds and manure and carcass of birds and fish, respectively), both study adopted a 90 days composting period. Bui et al. (2015), added pisciculture sludge to macrophytes in the Vietnam composting process, concluded the process at 45 days. These authors presented similar conclusions regarding the feasibility of using macrophytes in the composting process, attributing to this plant species an additional source of nitrogen to final compost.
Some studies adopted a consortium with conventional composting (composting with manual turning) and vermicomposting. Gupta et al. (2007) and Pramanik (2010) used conventional composting as a pretreatment of the compost, prior the beginning of vermicomposting process. This pre-treatment was performed over 7 days, in the developed study by Pramanik (2010), and for 21 days in the case of Gupta et al. (2007). The divergence in pre-treatment periods is attributed to the main objective of each study, being that of Pramanik (2010) to evaluate the microbiology involved in the process of composting macrophytes, and that of Gupta et al. (2007) the feasibility of using organic fertilizer from vermicomposting of cattle manure and macrophytes.
Some of the authors who have adopted the composting, with macrophytes, by natural aeration have reinforced the importance of humidity from the composed throughout process. The partial dehydration of macrophytes, prior to the beginning of the composting process was performed by Some of the authors highlight qualities attributed to the final composting, resulting of macrophytes composition, as the increased in N, P and K concentrations , Goswami et al. (2017). The metals presence in macrophytes composition is attributed, however, to the increase in content of potentially toxic elements throughout the composting  Varma et al. (2017) is the only author to describe the use of forced aeration process. Using as sources of biomass, the cattle manure and sawdust, in addition to the macrophytes, the authors compare different scenarios -by turning, composting for soil aeration, passive and forced aeration. The authors conclude that the best results of the first two types of aeration are due to the better distribution of air in the material bed.  There were still 22 (≈27%) studies that did not specify the macrophyte species applied in the study, however given the introductory chapter of articles it is possible to infer that part of this percentage was referring mainly to the macrophyte species Eichhornia crassipes.
According to information available in Sharma et al. (2016), Eichhornia crassipes have oval leaves, wide, thick, shiny and could grow above the water surface up to 1 m in height. The leaves have 10 to 20 cm in diameter. They have long stems, spongy and bulbosus. Each plant consists of a rosette of six to ten sheets attached to a rhizome with a fibrous root system well developed.
These studies, however, had their main focus on parameters evaluation of the macrophyte composting process. The other articles, mainly focused on the quality/application of the final compost, had complementation of organic and/or mineral matter. The materials used in addition to the macrophytes in composting are illustrated quantitatively, related to the number of articles where they were applied, in Figure 5.

Compost monitoring
The composting monitoring process, performed by the authors identified in the literature review, occurred, in most cases, before proceeding with materials analysis that would be composted, along process and in the final compost.  The main parameters stages analyzed (before, during and after the composting) resemble. The physical and chemical parameters more analyzed are pH, electrical conductivity (EC) and Humidity. In a less expressive amount, however, still standing out above the others, the content of Organic Matter (OM) and Total Kjeldahl Nitrogen (TKN) are also among the most adopted by the authors.
The most adopted macronutrients in monitoring are K, N and P, the latter two being, however, surpassed in organic carbon monitoring during/after composting, also significantly adopted in monitoring prior to composting. Is also adopted C/N ratio by a large number of the authors, and its prior monitoring to composting held to be maintained at close values to ideal for process and during/after composting verifying compost maturity (Araiza et al. , 2016;Nath and Singh, 2016;Pushpa et al., 2016a;Bisen et al., 2017).
Among the micronutrients, the elements Zinc (Zn), Copper (Cu) and Iron (Fe) stand out in decreasing order, both in the previous monitoring and during/post composting. They are also monitored in some of the micronutrient articles such as Manganese (Mn), Sodium (Na), Nickel (Ni) and, in low expressive percentages, Boron (B) and Cobalt (Co).
Due to the macrophytes chemical elements assimilation characteristics (Ganesh et al., 2012;Singh and Kalamdhad, 2012;Singh and Kalamdhad, 2014;Mazumder et al., 2020), plant toxic elements monitoring, prior to composting, and the residual of these elements in the compound, during/after process composting, is adopted in part of the studies. Elements such as Pb, Cr and Cd are the most monitored in the articles identified in this literature review, and elements such as Hg and Arsenic (As) are also analyzed. The potentially toxic element type present in macrophytes may differ, depending on local proliferation characteristics. Thus, even that lead, chromium and cadmium are main elements potentially toxic monitored, others can be adopted.
The grouped parameters named "Others" correspond to a not framed indicators in other divisions. Some of these parameters are associated with the type of study being conducted, such as specific studies of microbiology and its influence on the composting process (Pramanik, 2010;Bisen et al., 2017;Vishan et al., 2017), analysis of the decomposition of the woody fraction of macrophytes (Sarika et al., 2014;Devi et al., 2015;Das et al., 2016) or its application and potential environmental damage, to human beings and economic development (Rezania et al., 2015a;Sharma et al., 2016).

Final remarks
The macrophyte composting process interest is a theme continuously addressed around the world in recent years, having evolved from the focus on analyzing the feasibility of the composting process to concerns about the characteristics, mainly of toxicity, of the compost produced.
On identified studies, the spatial distribution in literature review highlights management problem for this plant type is not restricted to continental countries, such as China, India, USA or Brazil. Environmental, economic and social impacts results from macrophyte proliferation's in water resources, have being object of studies in several countries around the world.
Composting with natural aeration predominates in the literature reviewed, representing 56% (half of this one, feature composting time equal to or less than 60 days) followed by vermicomposting (25%). In general, the authors consider it necessary to maintain humidity in the composting process around 60%.
Macrophytes partial dehydration, before composting process beginning seems to be crucial to ensure near-ideal humidity values.
Eichhornia crassipes corresponded to approximately 69% of the scientific researches and the special distribution, can be considered a worldwide problem.
Macrophytes chemical composition depends on where it developed, therefore, knowing the environment where it is inserted is essential to identify possible chemical elements (nutritional or dangerous) that may be in the plant's biomass.
Cellulose significant percentage that compose the macrophytes can prolong composting process. Thus, practices such as the previous comminution of plants and / or cellulose-degrading inoculants addition throughout composting process can represent peculiar composting stages this plant type resulting from the knowledge acquired in past researches.
Composting process operational parameters are not standardized in the accessed studies, lacking adjustments, according to each scientific researches context.
The macrophyte composting studies evolution have evolved into compound production with heavy metals lesser amount in their soluble forms. Micro and macro nutrients richness can be considered for next evolutionary composting studies stage for this plant type, either by organic matter sources characteristics and/or mineral sources addition.