**2. Biogas production from water hyacinth**

Water hyacinth (*Eichhornia crassipes*) is a water plant that grows in swamps, lakes, reservoirs, and rivers and that flows calmly. The leaves of the water hyacinth are bright green, have an ovate shape, and widen with a diameter of up to 15 cm [10]. The water hyacinth (*Eichhornia crassipes*) is generally considered as a waterweed, which has become a problem that damages the environment, the system irrigation, and agriculture [11]. Water hyacinth is a type of weed that grows very fast. The growth of water hyacinth can reach 1.9% per day with a height between 0.3 and 0.5 m. Its rapid growth is felt to be very detrimental because water hyacinth plants that covered the surface of the water will cause the oxygen content to decrease [12].

### *Biogas Production from Water Hyacinth DOI: http://dx.doi.org/10.5772/intechopen.91396*

Water hyacinth has attracted attention to scientists to use it as a potential biomass because its rich in nitrogen, essential nutrients, and high fermentation contents [13].

In Indonesia, most of the major lakes are also facing environmental problems such as eutrophication, sedimentation, and a decline in surface area. Indonesia has determined that 15 lakes have become a national priority to be restored and preserved [14]. Behind its beauty, Rawa Pening Lake keeps a pile of concerns. The 2667 hectare natural reservoir located in Ambarawa, Bawen, Tuntang, and Banyubiru, Semarang Regency, is currently being staked out by sedimentation, not to mention the uncontrolled growth of water hyacinth that takes up lake land. The decline in water storage capacity due to the sedimentation process results in a decrease in reservoir function and effectiveness. Rawa Pening Lake has even been included in the list of 15 critical lakes in Indonesia [15].

Rawa Pening Lake has been facing an invasion of macrophytes indicated by a massive growth of water hyacinth that covers more than 40% of the lake surface [16]. Although the water hyacinth is often used, it does not reduced. Their growth is so fast causing water hyacinth plants become into waterweeds. Water hyacinth is being utilized as a biogas raw material because it has carbohydrate and cellulose contents. Cellulose will be hydrolyzed into glucose by bacteria which will produce methane gas as biogas [10]. An image of a massive growth of water hyacinth in Rawa Pening Lake, Indonesia, is shown in **Figure 1**.

Biogas contains methane, and it is the combustion of methane which constitutes the energy component of biogas [7]. It consists mainly of methane (CH4) and carbon dioxide (CO2) and is formed from the anaerobic bacterial decomposition of organic compounds, i.e., without oxygen. The gases formed are the waste products of the respiration of these decomposer microorganisms, and the composition of the gases depends on the substance that is being decomposed. If the material consists of mainly carbohydrates, such as glucose and other simple sugars and high molecular compounds (polymers) such as cellulose and hemicellulose, the methane production is low. However, if the fat content is high, the methane production is likewise high [17].

**Figure 1.** *A massive growth of water hyacinth in Rawa Pening Lake, Central Java, Indonesia.*

Biogas may be used in many different ways:


There were a lot of researches about biogas production that used various parameters that effected to it. These were food to microorganism (F/M) ratio, carbon to nitrogen (C/N) ratio, and total solid (TS). In the production of biogas from anaerobic digestion, the value of the food to microorganism (F/M) ratio shows the ratio between the mass of food available in the substrate and the mass of microorganisms that act as decomposers. A food to microorganism (F/M) ratio that is too small can cause microbes to be not metabolized completely, and if the value of the F/M ratio is excessive, it results in an unbalanced metabolism [18].

In addition to the organic content of the substrate, the carbon to nitrogen (C/N) ratio was stated as an important factor for the biogas process. The C/N ratio should be in the range between 10 and 30 and, as an optimal ratio, between 25 and 30 for digesters operating at full potential. When the C/N ratio is low, there is a risk of ammonia obstruction, the process of methanogenesis being more sensitive. High ratios can lead to low methane yields equivalent to the lack of nitrogen available for cell growth [19].

According to Brown and Li (2013) in the production of biogas from biomass raw materials, lignocellulose is appropriate to be produced from using the SS-AD method because lignocellulosic biomass has a total solid concentration of >15% and has low moisture content. According to Malik (2006) water hyacinth contains 95% water and consists of networks that are hollow, and this is the reason why L-AD method is well applied to water hyacinth because of its TS content which is relatively low [20].

Some researches about biogas production of water hyacinth have been done by students of the Environmental Engineering Diponegoro University. The researches were about biogas production from water hyacinth using liquid anaerobic digestion (L-AD) and solid-state anaerobic digestion (SS-AD). The part that was used from water hyacinth was the leaves.

### **2.1 Measurement methods**

### *2.1.1 Preliminary methods*

Preliminary methods were conducted before doing the main researches to know about the contents of each component that will be used. Various parameters will be used in biogas researches.

### *2.1.1.1 Total solid*

According to the American Public Health Association (APHA) standard method, the formula for total solid content can be seen in Eq. (1):

*Biogas Production from Water Hyacinth DOI: http://dx.doi.org/10.5772/intechopen.91396*

 $ ${}^{\text{ath}}$ $   $ ${}^{\text{spin}}$ $   $ ${}^{\text{spin}}$ $   $ ${}^{\text{spin}}$ $   $ ${}^{\text{spin}}$ $   $ ${}^{\text{spin}}$ $   $ ${}^{\text{spin}}$ $   $ ${}^{\text{spin}}$ $   $ ${}^{\text{spin}}$ $ 

Description: *W*1, cup weight; *W*2, cup weight and sample weight; *W*3, cup weight and sample weight after being ovened.
