Pius M. Ndegwa

Effects of stocking density and feeding rate on vermicomposting of biosolids

Abstract The double-pronged problem of quantity, and disposal of waste streams from a myriad of industries, is becoming increasingly acute, the world over. The use of earthworms as a waste treatment technique for such wastes is gaining popularity. This method is commonly known as vermicomposting. Compared to conventional microbial composting, vermicomposting produces a product that is more or less homogenous, with desirable aesthetics, with reduced levels of contaminants and tends to hold more nutrients over a longer period, without impacting the environment. Like in other related waste treatment techniques, certain parameters need to be established for the design of efficient and economical vermicomposting systems. Specifically, the focus of this study was to investigate and establish an optimal stocking density and an optimal feeding rate for the vermicomposting of biosolids, with paper mulch provided as bedding. A stocking density of 1.60 kg-worms/m 2 (0.33 lb-worms/ft 2 ) and a feeding rate of 1.25 kg-feed/kg-worm/day resulted in the highest bioconversion of the substrate into earthworm biomass. The best vermicompost was obtained at the same stocking density and a feeding rate of 0.75 kg-feed/kg-worm/day.

Integrating composting and vermicomposting in the treatment and bioconversion of biosolids.

Traditional thermophilic composting is commonly adopted for treatment of organic wastes or for production of organic/natural fertilizers. A related technique, called vermicomposting (using earthworms to breakdown the organic wastes) is also becoming popular. These two techniques have their inherent advantages and disadvantages. The integrated approach suggested in this study borrows pertinent attributes from each of these two processes and combines them to enhance the overall process and improve the products qualities. Two approaches investigated in this study are: (1) pre-composting followed by vermicomposting, and (2) pre-vermicomposting followed by composting. The substrate was biosolids (activated sewage sludge) with mixed paper-mulch as the carbon base. Eisenia fetida (red wigglers) was the species of earthworms used in the vermicomposting processes. The results indicate that, a system that combines the two processes not only shortens stabilization time, but also improves the products quality. Combining the two systems resulted in a product that was more stable and consistent (homogenous), had less potential impact on the environment and for compost-vermicomposting (CV) system, the product met the pathogen reduction requirements.

Effects of C-to-N ratio on vermicomposting of biosolids.

The role of organic carbon and inorganic nitrogen for cell synthesis, growth, and metabolism is important in all living organisms. To provide proper nutrition for earthworms during vermicomposting, carbon and nitrogen must be present in the substrates at the correct ratio. The usual practice is to arbitrarily add either a rich nitrogenous material, or a rich carbonaceous material to the feed substrate, depending on the situation, to correct for C-to-N imbalance. In addition, the conventional determination of C-to-N ratio is not always based on the proportion of each nutrient that is available for these processes, but on their absolute content in the substrate. More so, diAerent earthworm species are impacted diAerently by C-to-N ratio and feed mixture type. Therefore, pilot studies are necessary to establish optimal C-to-N ratio for a specific earthworm species and a specific feed mixture. Specifically, the focus of this study was to investigate and establish a suitable C-to-N ratio for vermicomposting of fresh biosolids (activated sewage sludge) amended with paper mulch, using Eisenia fetida. An optimal stocking density of 1.60 kg-worms/m 2 and an optimal feeding rate of 0.75 kg-feed/kg-worm/day (Ndegwa, P.M., Thompson, S.A., Das, K.C., 1999. Biores. Technol. 71 (1), 5‐12), were used in this study. A C-to-N ratio of 25 resulted in the highest stability of the product, the best fertilizer-value of the product, and also a product with the lowest potential for environmental pollution. ” 2000 Elsevier Science Ltd. All rights reserved.

Effect of lauric acid and coconut oil on ruminal fermentation, digestion, ammonia losses from manure, and milk fatty acid composition in lactating cows

This experiment (replicated 3 x 3 Latin square design) was conducted to investigate the effects of lauric acid (LA) or coconut oil (CO) on ruminal fermentation, nutrient digestibility, ammonia losses from manure, and milk fatty acid (FA) composition in lactating cows. Treatments consisted of intraruminal doses of 240 g of stearic acid/d (SA; control), 240 g of LA/d, or 530 g of CO/d administered once daily, before feeding. Between periods, cows were inoculated with ruminal contents from donor cows and allowed a 7-d recovery period. Treatment did not affect dry matter intake, milk yield, or milk composition. Ruminal pH was slightly increased by CO compared with the other treatments, whereas LA and CO decreased ruminal ammonia concentration compared with SA. Both LA and CO decreased protozoal counts by 80% or more compared with SA. Methane production rate in the rumen was reduced by CO compared with LA and SA, with no differences between LA and SA. Treatments had no effect on total tract apparent dry matter, organic matter, N, and neutral detergent fiber digestibility coefficients or on cumulative (15 d) in vitro ammonia losses from manure. Compared with SA, LA and CO increased milk fat 12:0, cis-9 12:1, and trans-9 12:1 content and decreased 6:0, 8:0, 10:0, cis-9 10:1, 16:0, 18:0, cis 18:1, total 18:2, 18:3 n-3 and total polyunsaturated FA concentrations. Administration of LA and 14:0 (as CO) in the rumen were apparently transferred into milk fat with a mean efficiency of 18 and 15%, respectively. In conclusion, current data confirmed that LA and CO exhibit strong antiprotozoal activity when dosed intraruminally, an effect that is accompanied by decreases in ammonia concentration and, for CO, lowered methane production. Administration of LA and CO in the rumen also altered milk FA composition.

Effect of dietary concentrate on rumen fermentation, digestibility, and nitrogen losses in dairy cows.

The objective of this experiment was to investigate the effect of level of dietary concentrate on rumen fermentation, digestibility, and N losses in lactating dairy cows. The experiment was a replicated 3x3 Latin square design with 6 cows and 16-d adaptation periods. Ruminal contents were exchanged between cows at the beginning of each adaptation period. Data for 2 of the diets tested in this experiment are presented here. The diets contained (dry matter basis): 52% (LowC; control) and 72% (HighC) concentrate feeds. Crude protein contents of the diets were 16.5 and 16.4%, respectively. The HighC diet decreased ruminal pH and ammonia concentration and increased propionate concentration compared with LowC. Acetate:propionate ratio was greater for LowC than for HighC. Rumen methane production and microbial protein synthesis were unaffected by diet. Dry matter intake was similar among diets, but milk yield was increased by HighC compared with LowC (36.0 and 33.2 kg/d, respectively). Milk fat percentage and yield and total-tract apparent NDF digestibility were decreased by HighC compared with LowC. More ruminal ammonia N was transferred into milk protein with HighC than with LowC. Urinary N excretion, plasma urea N, and milk urea N concentration were not affected by diet. The ammonia emitting potential of manure was similar between LowC and HighC diets. Increased concentrate proportion in the diet of dairy cows resulted in reduced ruminal ammonia concentration and enhanced ammonia utilization for milk protein synthesis. These effects, however, did not result in reduced urinary N losses and only marginally improved milk N efficiency. Increasing dietary concentrate was not a successful strategy to mitigate enteric methane production and ammonia emissions from manure.

Bioremediation of oil-contaminated soil using Candida catenulata and food waste

Even though petroleum-degrading microorganisms are widely distributed in soil and water, they may not be present in sufficient numbers to achieve contaminant remediation. In such cases, it may be useful to inoculate the polluted area with highly effective petroleum-degrading microbial strains to augment the exiting ones. In order to identify a microbial strain for bioaugmentation of oil-contaminated soil, we isolated a microbial strain with high emulsification and petroleum hydrocarbon degradation efficiency of diesel fuel in culture. The efficacy of the isolated microbial strain, identified as Candida catenulata CM1, was further evaluated during composting of a mixture containing 23% food waste and 77% diesel-contaminated soil including 2% (w/w) diesel. After 13 days of composting, 84% of the initial petroleum hydrocarbon was degraded in composting mixes containing a powdered form of CM1 (CM1-solid), compared with 48% of removal ratio in control reactor without inoculum. This finding suggests that CM1 is a viable microbial strain for bioremediation of oil-contaminated soil with food waste through composting processes.

The effects of ruminally degraded protein on rumen fermentation and ammonia losses from manure in dairy cows

This experiment investigated the effect of dietary crude protein (CP) and ruminally degraded protein (RDP) levels on rumen fermentation, digestibility, ammonia emission from manure, and performance of lactating dairy cows. The experiment was a replicated 3 x 3 Latin square design with 6 cows. Three diets varying in CP concentration were tested (CP, % of dry matter): 15.4 (high CP, control), 13.4 (medium CP), and 12.9% (low CP). These diets provided metabolizable protein balances of 323, -44, and 40 g/d and RDP balances of 162, -326, and -636 g/d (high, medium, and low, respectively). Both the medium and low CP diets decreased ruminal pH compared with high CP, most likely because of the higher nonfiber carbohydrate concentration in the former diets. Ruminal ammonia pool size (rumen ammonia N was labeled with (15)N) and the concentration of total free amino acids were greater for the high CP diet than for the RDP-deficient diets. Apparent total-tract nutrient digestibilities were not affected by treatment. Both the medium and low CP diets resulted in lower absolute and relative excretion of urinary N compared with the high CP diet, as a proportion of N intake. Excretion of fecal N and milk yield and composition were not affected by diet. Milk N efficiency (milk N / N intake) and the cumulative secretion of ammonia-(15)N in milk protein were greater for the RDP-deficient diets, and milk urea N concentration was greater for the high CP diet. Both medium and low CP diets decreased the irreversible loss of ruminal ammonia N compared with the high CP diet. The rate and cumulative ammonia emissions from manure were lower for the medium and low CP diets compared with the high CP diet. Overall, this study demonstrated that dairy diets with reduced CP and RDP concentrations will produce manure with lower ammonia-emitting potential without affecting cow performance, if metabolizable protein requirements are met.

Nitrogen losses from dairy manure estimated through nitrogen mass balance and chemical markers

Ammonia is an important air and water pollutant, but the spatial variation in its concentrations presents technical difficulties in accurate determination of ammonia emissions from animal feeding operations. The objectives of this study were to investigate the relationship between ammonia volatilization and delta15N of dairy manure and the feasibility of estimating ammonia losses from a dairy facility using chemical markers. In Exp. 1, the N/P ratio in manure decreased by 30% in 14 d as cumulative ammonia losses increased exponentially. Delta 15N of manure increased throughout the course of the experiment and delta15N of emitted ammonia increased (p<0.001) quadratically from -31 per thousand to -15 per thousand. The relationship between cumulative ammonia losses and delta15N of manure was highly significant (p<0.001; r2=0.76). In Exp. 2, using a mass balance approach, approximately half of the N excreted by dairy cows (Bos taurus) could not be accounted for in 24 h. Using N/P and N/K ratios in fresh and 24-h manure, an estimated 0.55 and 0.34 (respectively) of the N excreted with feces and urine could not be accounted for. This study demonstrated that chemical markers (P, K) can be successfully used to estimate ammonia losses from cattle manure. The relationship between manure delta15N and cumulative ammonia loss may also be useful for estimating ammonia losses. Although promising, the latter approach needs to be further studied and verified in various experimental conditions and in the field.

Optimization of anaerobic sequencing batch reactors treating dilute swine slurries.

Use of anaerobic digestion for the treatment and recovery of biogas from concentrated animal waste effluents is a technically viable approach, but widespread acceptance has been limited due to poor economics. This challenge is magnified several-fold when considering anaerobic digestion of low-strength or dilute animal slurries because of the larger digester volumes and the corresponding high energy input requirements. These constraints could be mitigated by using an anaerobic sequencing batch reactor (ASBR). This technology has shown tremendous potential to improve the economics for the treatment of dilute animal waste effluents. This article reports preliminary optimization (biogas production and organic strength reduction) of an ASBR treating dilute swine slurries from pit-recharge manure management systems commonly found in confined swine housing. Based on the results, optimum biogas yields from anaerobic digestion of low-strength swine waste (0.3% to 0.4% TS) were approximately 0.14 mL/mg COD and 0.16 mL/mg COD at 5.25 and 6 days HRT at digestion temperatures of 20°C and 35°C, respectively. Higher operational temperature improved the specific biogas yield, but the qualities of biogas produced at the two temperatures, although high (65% to 70% CH4 and 17% to 20% CO2), were not significantly different. Maximum COD reductions of approximately 90% and 84% would be achieved at 7.2 and 9.1 days HRT at digestion temperatures of 20°C and 35°C, respectively. Higher COD reduction (implying more bio-stabilization of slurry) in the lower-temperature digester was attributed to less biomass washout, which is likely due to more efficient solids settling. The volatile fatty acids at both reactor temperatures were reduced from a mean of 639 ±75 mg/L in the influent to mean values of 74 ±12 and 85 ±17 mg/L in the effluents at 20°C and 35°C, respectively, which significantly mitigated the potential of odor generation from the effluents. Additionally, it was observed that the nutrient (both N and P) levels in the effluents remained about the same as in the influent.

Effect of Solid-Liquid Separation on BOD and VFA in Swine Manure

Fresh swine manure was sieved into seven different particle size categories, i.e., <0.075 mm, < 0.15 mm, < 0.25 mm, < 0.5 mm, < 1.0 mm, < 1.4 mm, and < 2.0 mm. Manure was stored in seven PVC columns and sampled every 5 days up to 30 days. Manure samples were analyzed for total volatile fatty acids (VFAs), 5-day biochemical oxygen demand (BOD5), total solids (TS), total suspended solids (TSS), and total volatile solids (TVS). Two parameters (VFAs and BOD5) were used to determine the odor generation potential of the test manure. The results showed that total VFAs correlated well with BOD5 (R 2 = 0.8297). The levels of TSS only explained 40% of BOD5 and 46% of VFAs, both of which increased with storage time, regardless of solid particle sizes. Also, the data inferred that most of the odorous compounds (measured by VFA and BOD levels) were contained in manure solid particles less than 0.075 mm. These cannot be removed by commercial mechanical separators with screen size ranging from 0.5 to 3.0 mm. With an average separation efficiency of 25% for most commercially available mechanical separators, the removal efficiencies of BOD5 and VFAs were as low as 10% and 12%, respectively. These findings cannot justify the use of solid-liquid separation to control odor. Data also showed that for swine manure, it is critical to run separation treatment within the first ten days after the manure is excreted to potentially improve the separation efficiency. After ten days, the degradation of TSS was accelerated due to the increased biological activities, which may greatly reduce the separation efficiency.