Goat manure formula in sludge cake wastewater treatment plant as organic fertilizer

. The use of activated sludge in wastewater treatment plants (WWTP) in industry gives a by-product in the form of sludge cake. Sludge cake presents a new problem for the environment because its accumulation causes the land to become unproductive, disrupts aesthetics, increases microbial activity, and pollutes water and soil, which can be harmful to humans and the environment. PT X is one of the industries that produces 80 kg/day of sludge cake. Based on laboratory results, X WWTP sludge cake has the potential to be used as an organic fertilizer. However, the use of sludge cake as organic fertilizer does not meet fertilizer quality standards and does not provide optimal results for plants. Goat manure is known to increase the organic fertilizer content of sludge cake in accordance with fertilizer quality standards. This research aims to find the best formula for adding goat manure to WWTP sludge cake which is carried out using four treatments, namely sludge cake without treatment, and the addition of goat manure 1.4 kg, 2.1 kg, and 2.8 kg. The stages of the research include the preparation of raw materials, the manufacture of organic fertilizers, and testing the content of organic fertilizers. The results showed that there was an increase in physical and chemical parameters on organic fertilizers, namely pH (6.6), C (22.14%), N (3.55%), P (4.65%), K (0.45%), Ca (0.52%), and Mg (0.26)), as well as a decrease in water content (15.40%) at the end of composting. The addition of goat manure with a combination of other additives to X TWP sludge cake can meet organic fertilizer quality standards. The addition of 2.1 kg of goat manure is the best formula to increase organic fertilizer.


Introduction
A wastewater treatment plant (WWTP) is a system for processing contaminated wastewater into water that meets quality standards so that it is safe to return to the water cycle [1].Today, one of the WWTP methods most widely used in industry is the activated sludge system.Activated sludge is a colony of microorganisms that lives in a suspended state, grows to form flocks, and has the ability to treat wastewater [2].The use of activated sludge in WWTP can cause new problems with the presence of by-products in the form of sludge cake.The sludge cake is a mixture of organic material suspension and microbial colonies that has gone through a pressing process (reducing water content) to become a solid (sludge cake).Sludge cake that is not processed further will have negative impacts on the company and the surrounding environment.Accumulation of sludge cake will certainly disturb the aesthetics of the company area, requiring large areas of land to accommodate the waste, as well as transportation costs for moving the sludge cake waste.The accumulation of sludge cake also causes environmental pollution such as non-productive land, unpleasant odors due to microbial activity in the sludge cake, and heavy metal content that is harmful to humans and the environment.
The application of the activated sludge system at PT X WWTP also cannot be separated from by-products in the form of sludge cake.The sludge cake produced by PT X WWTP can reach 80 kg of sludge cake/day.WWTP sludge cake can be used as an organic fertilizer because it contains high levels of organic and mineral materials.The composition of organic fertilizer with a mixture of 30% phosphate: 40% sludge cake: 30% cow manure has been proven to be able to increase levels of C-organic, phosphate, and C/N ratio.However, in practice, this formulation turned out to reduce total N and K levels in organic fertilizer.The decrease in N-total in the final result of organic fertilizer is due to the low nitrogen content in the added cow dung, whereas during composting, 5% of the nitrogen will be lost to become gas.Apart from that, nitrogen in fertilizer is also used by microorganisms for their growth process [3].Nitrogen absorbed by microorganisms will be used in the formation of proteins, nucleic acids, and coenzymes as a physiological function of microorganisms that supports their activities in decomposing organic materials [4].The decrease in potassium in organic fertilizer can also be caused by the use of potassium by microorganisms as a catalyst in the decomposition of organic materials [5].Overall, research on WWTP sludge cake as organic fertilizer carried out by [1] still does not meet fertilizer quality standards.Therefore, it is necessary to carry out further formulation to improve the quality of organic fertilizer from sludge cake so that it meets organic fertilizer quality standards.
X WWTP sludge cake has a water content of 53.30%, C-organic 21.01%, P 2.68%, K 0.06%, N-total 4.53%, and C/N ratio of 4.64.The K value and C/N ratio of the X WWTP sludge cake are relatively low, so they need to be increased further to meet fertilizer quality standards.By combining the research methods of [1], a further formulation was carried out using additional ingredients to increase the K content and C/N ratio in the X WWTP sludge cake which will be used as an organic fertilizer.The use of dry leaves and goat manure is known to increase the nitrogen, potassium, and C/N ratio content of organic fertilizer.According to [6], dry leaves have a C/N ratio of 50-60 which, if mixed with mud and composted for 3-4 weeks, will balance the organic fertilizer ratio (C/N ratio 10-25).The composition of adding dry leaves to the best organic fertilizer is 30%.Goat manure contains 1.5% N, P 0.13%, and K 1.8%.Goat manure has a higher nitrogen and potassium content than other manure [7].The best sludge cake composition according to research by [1] is 40%.Thus, goat manure was formulated in the X WWTP sludge cake as organic fertilizer so that its quality could be improved in accordance with organic fertilizer quality standards.This research was conducted to find the best organic fertilizer formulation from sludge cake combined with goat manure.The results of organic fertilizer are then measured by physical parameters in the form of pH and water content, as well as chemical parameters in the form of organic C, N, P, K, Ca, and Mg.

Material and methods
This research was carried out using 4 treatments, namely K0 = sludge cake without treatment, K20 = addition of 1.4 kg of goat manure, K30 = addition of 2.1 kg of goat manure, and K40 = addition of 2.8 kg goat manure (the weight of the goat manure variations is based on 20% (K20), 30% (K30), and 40% (K40) of the 7 kg total weight of the formula to be made).Treatments K20, K30, K40 added 2.4 kg of sludge cake and 2.1 kg of dry leaves.This research went through the stages of preparing raw materials, making organic fertilizer, and testing the organic fertilizer content.

Preparation of research materials
Material preparation needs to be done first before making organic fertilizer from sludge cake.The water content of the sludge cake is reduced to 40-50% using direct sunlight or a rotary dryer, with periodic turning to maintain aeration.Goat manure is selected that is old (>2 weeks) and has the characteristics of being odorless, crumbly, and low temperature.EM4 as a bioactivator needs to be activated first by weighing 100 grams of potato, cutting it into small pieces, adding 500 mL of water, and heating for 15 minutes over medium heat until the extract comes out as indicated by the color of the potatoes fading and the water turning yellowish.The potato extract was cooled to room temperature and then mashed using a blender.Potato extract was put into a plastic jerrycan and added with 1.3 L of water, 100 mL of EM4 solution, and 100 mL of molasses.Stir until homogeneous and tightly cover the jerrycan.Jerrycan is placed in a shady place for 5 days.The lid is opened once a day to release CO 2 gas.Active EM4 is characterized by the appearance of small bubbles on the surface of the solution.Dry leaves are chopped into small pieces first to facilitate bacterial decomposition.

Making of organic fertilizer
Making organic fertilizer is done by mixing 2.4 kg of sludge cake and 2.1 kg dry leaves into each composting tank or reactor containing goat manure with variant concentrations of 1.4 kg (20%, K20), 2.1 kg (30%, K30), and 2.8 (40%, K40).Meanwhile, K0 is a sludge cake that has not been given any treatment.After mixing all the ingredients, spray 300 mL/treatment of active EM4 and then stir until homogeneous.The composting tank was closed and composted for 21 days by spraying active EM4 and regular stirring every 3 days.The end of the composting process is marked by organic fertilizer that is blackish brown in color, smells of earth or humus, and has a crumbly or easily crushed texture [8].Organic fertilizer is added with organominerals in the form of natural phosphate, active zeolite, and humus acid.Organic fertilizer with the addition of organominerals is left for 2 weeks to neutralize the condition of the fertilizer before being applied to plants.

Analysis of organic fertilizer
Analysis of organic fertilizer content was carried out based on physical and chemical parameters carried out by Balitkabi (Research Center for Nuts and Tuber Crops), Malang Regency, East Java.Analysis of physical and chemical parameters is carried out after the formulation has been composted and has become an organic fertilizer.Physical parameter analysis was carried out by calculating the pH and water content of organic fertilizer.pH is analyzed using an electromagnetic method, namely measuring the concentration of H+ ions in the soil solution and using the soil pH meter VT-05.Water content was analyzed using the gravimetric method, namely measuring the weight of water lost by weighing it before and after drying at a temperature of 105°C [9].
Chemical parameter analysis was carried out by calculating C-organic, N-total, P, K, Ca, and Mg.C-organic was analyzed using the Walkey and Black method, namely the oxidation of organic carbon by chromic and sulfuric acid to form chromium (III) which is equivalent to organic carbon and was measured using a spectrophotometer.N-total was analyzed using the Kjeldahl method, namely the destruction of nitrogen by sulfuric acid and selenium mixture to form ammonium sulfate, followed by distillation using an excess base, and the distillate formed was distilled.Nitrogen in the form of nitrate is extracted with water, reduced using devarda alloy, distilled, and then titrated again.P (P 2 O 5 ) levels were analyzed using a spectrophotometric method, namely P 2 O 5 extraction using wet oxidation of HNO 3 and HClO 4 , added ammonium molybdate and boric acid, reduced by ascorbic acid, and then measured using a spectrophotometer.(K 2 O) levels were analyzed using an atomic absorption spectrometer (AAS) or flame photometer which in principle calculates cation exchange by extracting the sample using NH 4 Oac and measuring the absorbance using SSA [9].Ca (CaO) and Mg (MgO) levels were analyzed using AAS which in principle calculates the absorbance of sample extraction due to the addition of LaCl 3 based on the Ca and Mg standard series [10].

Physical parameter analysis of organic fertilizer
The physical analysis results from the composted formula (organic fertilizer) showed that the K20, K30, and K40 treatments affected the pH and water content of organic fertilizer.The results of the analysis of the physical parameters of organic fertilizer provide different values for each sample, presented in Table 1.Note: K0 = organic fertilizer without treatment; K20, K30, K40 = organic fertilizer with 1.4 kg (20%), 2.1 kg (30%), and 2.8 kg (40%) of goat manure According to the analysis of physical parameters, organic fertilizer experienced an increase in pH during composting and had a final pH of 6.40-7.20.Organic fertilizer experienced an increase in pH value from the initial pH of 5.40, at K20, K30, and K40 respectively 1.30, 1.20, and 1.80.The increase in pH occurs due to the nitrification process by microorganisms, namely the oxidation process of ammonium to nitrate.Plants tend to absorb more nitrogen in the form of nitrate because nitrate has high mobility in the soil and is quickly bound by roots [11].According to Minister of Agriculture Decree Number 261/KPTS/SR.310/M/4/2019,solid organic fertilizer with added microbial treatment must have a pH of 4-9.Thus, this solid organic fertilizer meets the established quality standards for solid organic fertilizer.Good soil for plants has a pH close to 7 because in this condition the nutrients can dissolve in water, thereby increasing the absorption of nutrients by plants , 06001 (2024) BIO Web of Conferences https://doi.org/10.1051/bioconf/2024900600190 ICGAB 2023 [12].
After 21 days of composting, organic fertilizer had a water content value of 15%.This value experienced a decrease in water content of 19.90%, 37.90%, 37.90%, and 37.50% respectively at K0, K20, K30, and K40 from the initial water content of 53.30%.According to Minister of Agriculture Decree Number 261/KPTS/SR.310/M/4/2019,the water content in solid organic fertilizer enriched with microbes is 10-25%, so it meets quality standards.The decrease in water content at the end of composting is caused by the process of decomposing organic material by microorganisms, which causes the temperature to increase [5].The water content during the composting process must be controlled at optimal conditions (45-50% water content) so that the composting process runs optimally.Water content that exceeds 60% will cause anaerobic conditions so that air volume and circulation are low and smelly, and the decomposition process is hampered.Water content that is too low also inhibits the work of bacteria, so it is necessary to add water and stir the organic fertilizer being composted [13].

Chemical parameter analysis of organic fertilizer
The analysis of chemical parameters from the composted formula (organic fertilizer) shows that K20, K30, and K40 treatments provide an increase or decrease in several chemical parameters.The results of testing chemical parameters for organic fertilizer give different values for each sample and are presented in Table 2. Note: K0 = organic fertilizer without treatment; K20, K30, K40 = organic fertilizer with 1.4 kg (20%), 2.1 kg (30%), and 2.8 kg (40%) of goat manure The results of the chemical analysis showed that solid organic fertilizer had the highest C-organic in the K30 treatment, namely 22.14%, while the lowest C-organic was in the K40 treatment, namely 20.47%.Organic fertilizer experienced a decrease in Corganic in K0 and K40 respectively by 4.06% and 0.54% and an increase in K20 and K30 respectively by 0.38% and 1.13% from the initial C-organic value of 21.01%.The increase in C-organic value was caused by the addition of molasses during composting.Microorganisms prefer molasses as a carbon source compared to the main organic material because the carbon structure of molasses is simpler than organic material.The carbon needs of microorganisms are met with molasses so that organic materials are not degraded.
C-organic value can decrease due to the availability of C-organic material used by microorganisms as a source of nutrients to break down organic material and produce N, P, and K.The more C-organic is used, the more nutrients there are in organic fertilizer.In this case, the sample with the best C-organic content is the K40% sample with the lowest Corganic content.However, overall, all treatments containing C-organic have met the Corganic quality standards in Minister of Agriculture Decree Number 261/KPTS/SR.310/M/4/2019,namely a minimum of 15%.
The highest N-total content was in the K0 treatment, namely 4.64%, while the lowest N- total was in the K20% treatment, namely 3.42%.Organic fertilizer experienced a decrease in N-total in all treatments K0, K20, K30, and K40 respectively by 0.94%, 1.11%, 1.05%, and 0.98% from the initial N-total value of 4.53%.All treatments have met the quality standards for organic fertilizer N content in SNI 19-7030-2004, namely a minimum of 0.40%.The total N content in organic fertilizer is influenced by the raw materials and the composting process.Using raw materials with a high N-total will provide a high N-total value.The N element tends to be retained in organic fertilizer, but during the composting process, 5% of the N element will be lost as gas.Apart from that, the element N is also used by microorganisms for the needs of microorganism activities [14].
The highest P content was in the K30 treatment, namely 4.65%, while the lowest P was in the K0 treatment, namely 3.70%.Organic fertilizer experienced an increase in the P value in all treatments K0, K20, K30, and K40 respectively by 0.68%, 1.42%, 1.97%, and 1.78% from the initial P value of 2.68%.All treatments have met the quality standard for organic fertilizer P content in SNI 19-7030-2004, namely a minimum of 0.10%.The P element in all treatments increased at the end of composting.This is due to the decomposition process of organic material.After the composting process is complete, the microorganisms will die and the P in the microorganisms will mix with the compost fertilizer, so the P in the fertilizer will increase.The addition of phosphate fertilizer as an organomineral also increases P levels in organic fertilizer.
The highest K content had the same value in the K20, K30, and K40 treatments, 0.45%, while the lowest K content in the K0 treatment was 0.06%.Organic fertilizer experienced an increase in the K value in all K20, K30, and K40 treatments by 0.39% and a decrease in the K value in K0 by 0.01% from the initial K value of 0.06%.All treatments have met the quality standards for organic fertilizer K content in SNI 19-7030-2004, namely a minimum of 0.20%.During composting, the potassium element in the potassium dioxide (K2O) compound is used as a catalyst for microorganisms, thereby influencing bacterial activity.Bacteria and fungi will bind and store potassium in cells, which, when degraded, will provide potassium again [12].Apart from that, the increase in K levels is also caused by microorganisms' decomposition of organic matter [5].
The highest Ca content was in the K20 treatment, namely 0.52%, while the lowest Ca content was in the K0 treatment, namely 0.44%.Organic fertilizer experienced an increase in Ca values in all K20, K30, and K40 treatments by 0.52%, 0.50%, and 0.50% respectively, while K0 did not experience an increase or decrease in Ca values from the initial Ca value of 0.00011%.According to SNI 19-7030-2004, the quality standard for Calcium (Ca) content in compost is a maximum of 25.50%, so the calcium content in all treatments meets the quality standard but in low amounts.Calcium comes from the weathering of minerals and rocks contained in the soil.Low calcium levels in organic fertilizer can be caused by the materials used do not contain high levels of calcium, resulting in a Ca deficiency.The addition of dolomite after the composting process can overcome low Ca levels in organic fertilizer.Fine dolomite provides more effective results and faster reactions in increasing calcium availability [12].
The highest Mg content was in the K20 and K30 treatments, namely 0.26%, while the lowest Mg content was in the K0 treatment, namely 0.09%.Organic fertilizer experienced an increase in the Ca value in all K20, K30, and K40 treatments by 0.20%, while in K0 there was no increase or decrease in the Mg value from the initial Mg value of 0.09%.Based on SNI 19-7030-2004, the quality standard for magnesium content in compost is less than 0.60%, so all the treatments meet the quality standards.Magnesium comes from the weathering of magnesium minerals so that it is found freely in the soil.The availability of Mg in organic fertilizer is also influenced by pH, the higher the pH, the higher the binding of Mg [15].

Conclusion
Based on the analysis of the organic fertilizer content, it can be concluded that the best fertilizer content results were found in the K30 treatment, namely organic fertilizer with the addition of 2.1 kg (30%) of goat manure.This treatment can provide some of the best values for physical and chemical parameters, as well as meeting organic fertilizer quality standards.

Table 1 .
Physical parameters analysis of organic fertilizer.

Table 2 .
Chemical parameters analysis of organic fertilizer.