From the start, 2015 was ripe for world-changing innovation.

In early January, we saw Bill Gates drink clean water converted from sewer sludge and human waste by a special processor. In February, social workers and computer scientists came up with an algorithm to prevent the spread of HIV among homeless youth. In March, a research lab created a microchip that could actually help bridge the digital divide in developing countries.

See also: 7 incredibly simple inventions that are changing the world

And the revolutionary ideas and inventions tackling the world's most pressing problems kept coming throughout the year.

From a new sneaker that helps people with physical disabilities, to "nanosheets" that can absorb oil spills, to a bindi that delivers much-needed iodine to women in India, these are some of our favorite innovations that truly made a difference in 2015.

1. The machine that converts poop into clean drinking water

Approximately 2.4 billion people around the world didn't have access to basic, safe sanitation in 2015, while more than 660 million people used unimproved drinking water sources.

The Gates Foundation talked to engineers to figure out how we could use technology to tackle these issues. Peter Janicki, CEO of Janicki Bioenergy, developed a machine (shown in the video above) that converts sewer sludge into clean drinking water, electricity and pathogen-free ash in a matter of minutes.

The processor can help developing countries both by providing clean water and energy, as well as employing entrepreneurs to run it in the regions where it's needed most.

2. The algorithm that can prevent HIV among homeless youth

To prevent the spread of HIV among the homeless, USC researchers turn to math: http://t.co/FdNH5LgDx4 pic.twitter.com/F8yKOJdcZZ — USC (@USC) February 4, 2015

Homelessness affects about 2 million people between the ages of 13 and 24 every year in the United States — 11% of whom are HIV-positive. But researchers at the University of Southern California's Schools of Social Work and Engineering developed a new algorithm called PSINET, which uses artificial intelligence to identify the best person in a specific homeless community to spread important information about HIV prevention among youth.

Computer scientists mapped the friendships of homeless teens at a local homeless agency in Los Angeles. The algorithm looks at this network of friendships, and runs through thousands of possibilities for the person with the greatest reach at a certain point in time. That "peer leader" can then learn about basic information, like where to get tested for HIV, and in turn provide researchers with more information about the homeless community.

According to the researchers, PSINET spread 60% more information to communities than typical word-of-mouth campaigns.

3. The sneaker technology designed for people with disabilities

Image: Nike

In 2012, Matthew Walzer, who has cerebral palsy, wrote a letter to Nike asking the company to create sneakers that people with disabilities could easily put on and take off without the help of others. This year, the company announced a new line of footwear — Flyease — that has a zipper extending around the back of the shoe.

Instead of laces, which are incredibly difficult for people with movement disorders, stroke victims and amputees, the zipper allows you to "peel" it open with one hand and slide your foot in easily.

Nike's senior director of athlete innovation, Tobie Hatfield, designed the technology and worked with Walzer to develop and test the sneakers.

4. The life-saving device that can seal a wound in under a minute

Image: Mashable composite.REvMedX

Oregon startup RevMedX's new device XSTAT 30 is a syringe filled with tiny, biocompatible sponges, which can be injected into a deep wound to absorb blood and seal it in less than a minute. While it's been used on the battlefield since April 2014, it was recently approved by the FDA for civilian use.

A RevMedx researcher told PBS NewsHour that the sponges expand up to 15 times their size when they make contact with blood, which allows them to apply internal pressure to the walls of the wound cavity and block blood flow. The sponges would replace a medic's traditional method of deeply packing a wound with gauze and maintaining pressure.

5. The "Internet on a microchip"

The WiderNet Project, based at the University of North Carolina, Chapel Hill, developed the eGranary Pocket Library — a microchip that taps into the power of smartphones, laptops and tablets to deliver offline information and educational resources to billions of people without access to the Internet.

WiderNet has connected with with ministries of education, ministries of health and schools of information science in various countries, and aims to fill each "library on a chip" with a few thousand documents that a given institution, such as a medical school in Zambia, identifies as its core material.

The project reached its crowdfunding goal in May, and is collaborating with librarians, educators and volunteers around the world to pinpoint the information needed most.

6. Dinnerware that makes life easier for dementia sufferers

Image: Sha Yao/Eatwell

The cognitive and sensory impairments associated with dementia often result in difficulty eating — spills, confusion by intricate patterns on dinnerware and more — and out of frustration, sufferers often eat less than they should.

To tackle this issue, industrial designer Sha Yao created Eatwell, an eight-piece dining set that uses more than 20 distinct features to give dementia sufferers more independence during mealtime. For example, the dishware has slanted bottoms for easy scooping, bright colors to distinguish food and especially ergonomic utensils.

7. 3D-printed rotors that freeze seawater into drinking water

GE has long been expert in steam turbine technology for the desalination of water, but in 2015 it began to miniaturize the process.

A news release from the company explains:

"As part of the water desalination technology being developed with the [U.S. Department of Energy], researchers are using the same steam turbine turbomachinery 3D printed in a miniaturized form to compress and stream a mixture of air, salt and water through a hyper-cooling loop that freezes seawater. By freezing the mixture, the salt naturally separates in solid form, leaving just the ice. The ice is then melted, leaving clean water."

The design is a low-cost, low-energy way to create drinking water, and GE will continue to test the technology through mid-2016 to assess its feasibility.

8. The lamps powered by plants

Approximately 42% of rural areas in the Peruvian jungle don't have electricity, according to Peru's latest National Household Survey conducted by the National Institute of Statistics and Information.

The Universidad de Ingeniería y Tecnología (UTEC), which is known for developing innovative technologies in response to pressing world issues, created the Plantalámparas — a lamp that runs on plant power and lights the small village of Nuevo Saposoa.

During photosynthesis, the plant's waste decomposes in the soil, producing electrons during oxidation. The UTEC team captures these electrons by using electrodes in the soil and storing it in batteries. This process can light the LED bulbs for up to two hours.

9. A revolutionary material that could absorb large oil spills

Researchers at Deakin University in Australia, along with scientists at Drexel University in Philadelphia and Missouri University, developed a type of "nanosheet" that can clean up oil spills like a sponge. Each nanosheet is made up of flakes that are only several nanometers (one-billionth of a meter) thick with tiny holes, which can grow to the size of 5.5 tennis courts.

"The pores in the nanosheets provide the surface area to absorb oils and organic solvents up to 33 times its own weight," one of the researchers said.

The team developed an early-stage prototype of the idea in 2013, when it was a powder and didn't yet have a practical use.

10. The laundry device that lets washers reuse water for months

Washing machines use 20 gallons of water to remove one tablespoon of dirt. To conserve water and maintain efficiency, three graduate students at MIT invented AquaFresco, a type of filter that allows washing machines to reuse 95% of the water produced from each load.

The device filters out waste and recycles clean water and detergent for further cleaning cycles — up to six months' worth.

11. The durable, flat-pack housing for refugees

The Better Shelter is a temporary shelter created with refugees in mind, and has an expected lifespan of three years. It comes in flat packs, which means aid organizations can transport it efficiently and assemble it without tools. The designer created the shelters with family needs in mind, so each one includes a solar panel and lamp to provide light.

Better Shelter teamed up with the U.N. refugee agency UNHCR and the IKEA Foundation to use the shelters in the countries where refugees need them the most, such as Greece.

12. A low-cost device that simplifies auto-transfusion

In some developing countries, when patients hemorrhage blood during childbirth, doctors use a ladle and cheesecloth to perform auto-transfusion — gathering and recycling blood for the same patient during a medical procedure. This DIY method is necessary because the machinery and supplies typically used for transfusions are so costly.

Sisu Global Health's first device, the Hemafuse, is a low-cost product that makes the process simpler and more sanitary. It works like a hand-pump, sucking up blood and then passing it through a valve to a blood bag for later use. A filter removes clots and other particulates in the blood.

The Hemafuse won the 2015 Social Impact Prize at the SXSW Eco Awards in October and received a $100,000 investment from AOL cofounder Steve Case in September.

13. This 15-year-old's energy probe powered by ocean waves

Hannah Herbst from Boca Raton, Florida, won the 2015 Discovery Education 3M Young Scientist Challenge with her energy probe prototype, which seeks to "offer a stable power source to developing countries by using untapped energy from ocean currents."

The probe uses a 3D-printed propeller connected to a hydroelectric generator via a pulley system. The generator turns the movement of ocean waves through the propeller into usable electricity — a small amount that would be enough to power a desalination machine.

14. The prosthetic hand that can generate a sense of touch

Most prosthetics can't allow their wearers to regain their senses of touch, but DARPA's latest version of its prosthetic hand uses neurotechnology to do just that.

Researchers wired a 28-year-old man's prosthetic — a mechanical hand developed by the Applied Physics Laboratory (APL) at Johns Hopkins University — directly to his brain using electrodes on his sensory cortex and motor cortex. He became the first person to be able to "feel" physical sensations through a prosthetic hand, according to DARPA.

15. A simple toolkit to help girls wash and dry reusable pads

Product designer Mariko Higaki Iwai and a team of art students created Flo, a simple kit that allow girls in developing countries to easily wash, dry and carry reusable sanitary pads. Flo aims to ensure that girls don't miss school or work due to the stigma of menstruation, don't contract reproductive infections and illnesses, and also maintain confidence.

The product is essentially an enclosed basket spun between strings to wash sanitary pads and reduce drying time. The basket inside turns into a drying rack, and the kit also includes a carrying case to carry both new and old pads discreetly.

16. The student-made device helping babies breathe

According to the World Health Organization, acute respiratory illnesses are one of the leading causes of death among children under the age of five. Babies who have trouble breathing usually need Continuous Positive Airway Pressure (CPAP), a simple process that in developing countries sometimes only requires a tube submerged in water. But babies in severe respiratory distress require Nasal Intermittent Positive Pressure Ventilation (NIPPV), a process that often calls for costly machinery.

The NeoVent, which was created by undergrad students at Western Michigan University, uses an inverted bowl mechanism that oscillates to provide two levels of pressure needed to help babies breathe.

The device allows any medical center in the developing world equipped to perform CPAP adapt its machinery to perform NIPPV.

17. The eco-friendly brick that could revolutionize India

In India, there are hundreds of thousands of brick kilns producing close to 200 billion bricks per year — and the process contributes considerably to air pollution and greenhouse gas emissions. Paper mills also dump boiler ash in landfills, which affects both human and environmental health and has no practical use.

Tackling both issues head-on, students at MIT developed a new brick, called the Eco BLAC brick. The students made the brick from boiler ash using low-energy alkali activation technology rather than firing in a kiln.

In the end, the project recycles industrial waste into construction materials. The students are currently working in the city Muzaffarnagar, Uttar Pradesh, where they're partnering with a paper mill owner to implement a pilot plant on-site.

18. The printable strips for in-home testing of infectious diseases

Researchers at Florida Atlantic University have created paper and plastic strips for in-home diagnostic testing of HIV, E.coli, Staphylococcus aureas and other bacteria, as well as a smartphone app that could detect these bacteria using images remotely.

According to Fast Company, the E.coli test is made of paper (cellulose) and printed with a mixture of antibodies and gold nanoparticles. If bacteria is found, a color change indicates a positive result.

The plastic HIV test will begin trials at Brigham and Women's Hospital in Boston, and the researchers hope to commercialize the tests by mid-2016.

19. The bindi delivering much-needed iodine to impoverished women in India

Women in India traditionally wear a bindi — a small dot between the eyebrows — for religious purposes or to show they're married, but it's grown in popularity among all women.

Talwar Bindi's Life Saving Dot has an even higher purpose: vital health.

The Live Saving Dot is coated with iodine and delivers the recommended amount of 150-220 micrograms of the nutrient daily to poor women in India, where approximately 350 million people are at risk for iodine deficiency. A lack iodine can cause a number of health problems, especially during a woman's pregnancy.

Iodine can be absorbed through the skin, and the Life Saving Dot would be a particularly low-cost nutritional supplement — it costs only 10 rupees, or 16 cents, for a packet of 30 bindis. It has been distributed to women across rural India through health camps and clinics in several villages.

20. The beehive that harvests honey on its own

Two Aussie inventors created the Flow Hive beehive, which allows beekeepers to get honey on tap without opening the beehive and disturbing the bees.

The innovative hive's frames consist of partially formed honeycomb cells, which lets the bees complete the comb with their wax before filling the cells with honey. Beekeepers then need only turn a handle to split the cells vertically, so the honey can drip down to the base of the frame and out of the hive.

The Flow Hive has a clear window so you can watch the bees, which the inventors say can help with scientific research without disturbing them.

21. A smartphone dongle for 15-minute diagnostic tests

A team of researchers at Columbia University's School of Engineering has developed a low-cost smartphone dongle that can detect sexually transmitted infections from a finger prick of blood within 15 minutes.

Health care workers in Rwanda used the dongle in a pilot program by testing blood from 96 patients enrolled at prevention-of-mother-to-child-transmission clinics or voluntary counseling and testing centers. They only needed 30 minutes of training. Users just have to place the blood in the plastic collector, insert it into the microfluidic cassette, open the accompanying app, insert the cassette into the dongle and press the bulb to initiate flow. After 15 minutes, results are shown on the smartphone.

According to Smithsonian Magazine, the device costs $34.

22. This advanced treatment for jaundice in newborns

Jaundice is the primary reason why newborns are readmitted to hospitals worldwide, and millions are not receiving effective treatment.

Award-winning medical device nonprofit D-Rev launched its latest newborn product this year — Brilliance Pro, an advanced version of its Brilliance Classic product from 2012, which treats newborn jaundice with sophisticated phototherapy.

Brilliance Pro uses an integrated light meter, has expanded functionality and is sleeker to work better in the NICU. It retails at $400, and the distributor is Phoenix Medical Systems in India.

23. The best knee joint prosthetic for developing world amputees

In addition to newborn health, D-Rev also works on mobility. This year it launched the latest version of the ReMotion Knee, a high-performance prosthetic knee joint designed for people in the developing world.

The ReMotion Knee works with standard prosthetic leg systems and withstands humid and wet climates, and it's affordable at $80. So far, D-Rev has fit 7,351 amputees with the ReMotion Knee.

24. A temporary tattoo that helps diabetics track blood sugar

Patients with diabetes currently need to check their blood sugar multiple times per day with a painful finger prick. But nanoengineers at UC San Diego developed a temporary tattoo that non-invasively extracts and measures glucose levels in the fluid between skin cells.

The tattoo doesn't yet provide the necessary numerical levels, but the engineers say it will eventually have Bluetooth capabilities to garner such readouts. The method could pave the way for more uses of the technology, such as delivering medicines through the skin.

25. The ocean acidification sensor that revitalizes conservation

The Wendy Schmidt Ocean Health XPRIZE aimed to improve our understanding of how carbon dioxide emissions affect ocean acidification, which affects sea life and disrupts the food chain.

The winner of the competition, Sunburst Sensors, developed a breakthrough sensor that can withstand long-term monitoring of pCO2 and pH, and could prove instrumental in understanding ocean acidification and saving the oceans.

26. The app that helps blind people see through others' eyes

Be My Eyes is an iPhone app that allows users to "lend" their eyes to the blind. It connects blind users to volunteers around the world to use live video chat and have them describe what they see and answer any questions.

According to its website, the app has helped nearly 115,000 blind users so far.